Dark Mirror
The ultimate terror lies within… 

Dark Mirror is a Pocket TNG novel written by Diane Duane. Published by Pocket Books, it was first released in hardback in .

Summary 
From the book jacket (hardback edition)
Stardate 44010.2: the twenty-fourth century. Humanity's greatest dreams have become reality. Along with dozens of other sentient races, the people of Earth have formed the United Federation of Planets – a galactic civilization that governs much of the known universe for the good of all. Over the past two centuries, mankind has tamed its basest instincts, and reached the stars…But suppose it hadn't happened that way at all? Suppose instead humanity's darkest impulses, its most savage, animalistic desires had triumphed? Suppose the empire mankind made out in the stars was one ruled by terror, where only those willing to brutalize their own kind and their neighbors could survive?

One hundred years ago, four crewmembers of the  crossed the dimensional barrier and found a mirror image of their own universe, populated by nightmare duplicates of their shipmates. Barely able to escape with their lives, they returned, thankful that the accident which had brought them there could not be duplicated, or so they thought.But now the scientists of that empire have found a doorway into our universe. Their plan: to destroy from within, to replace one of our starships with one of theirs. Their victims: the crew of the .Here, from the author who gave us the smash New York Times bestseller Spock's World, is a dramatic Star Trek: The Next Generation adventure unlike any seen before. A story that shows us the crew of the Enterprise-D in mortal combat against the most savage enemy they have ever encountered… themselves.While on a scientific mission at the edge of the Milky Way Galaxy – where the phrase "empty space" can be taken quite literally – the  rendezvous with a ship from the nomadic Lailaru race, with whom a researcher from Starfleet has hitched a ride after a long research mission. The researcher, Commander "Hwii", has been studying hyperstrings – intangible connections between celestial bodies that seem to tie them together, and provide a sort of invisible "map" to the galaxy.

Shortly after the rendezvous, the Enterprise experiences a strange disturbance, and Hwii panics, insisting that his sense of direction tells them they are "not in the right place" despite the fact that their stellar position appears to be the same. The crew realizes what Hwii is talking about when an intruder is discovered tampering with the ship's computer core, a Lieutenant named Mark Stewart, who is an exact doppleganger for another Enterprise crewman.

Research into historical files lets the crew realize that the ship has been pulled into another universe, one that was first encountered by the crew of the original  a century earlier. Except, while that earlier crossover was an accident, this time the effect seems to have been produced on purpose. The Enterprises long-range sensors detect their counterpart: the ISS Enterprise-D. The ship carefully maintains its distance, while trying to determine the best way back home. Meanwhile, Mirror-Stewart dies from a virus that Crusher theorizes was designed by her counterpart, revealing that Mirror-Riker and Mirror-Troi did not expect him to return.

Eventually Picard's crew decides that the only way is to infiltrate the Imperial vessel and examine whatever apparatus they used to cause the transfer. La Forge and Troi are selected to carry out the mission – La Forge because of his computer skills, Troi because her counterpart's position as the ship's "security officer" would allow them unfettered access. However, the away team soon runs into difficulties which require that Picard join them aboard the Imperial vessel.

After Troi and La Forge incapacitate Picard's counterpart, and stash him in a closet aboard his quarters, they take refuge in an engineering crawlspace while Picard has to spend a day as "himself" aboard the Imperial vessel. It is a harrowing experience:
Picard is accompanied everywhere by his personal bodyguard, Reginald Barclay; when he is foolish enough to leave Barclay behind for a moment, he is nearly killed by a vengeful Wesley Crusher, seeking revenge for his father's murder at Picard's hands. Picard then has to watch mutely as Wesley is tortured in the ship's agony booth as punishment.
Will Riker is a thuggish brute and the "real" Deanna Troi a cold-blooded murderess with dangerously invasive telepathic abilities – and both wear their ambition to displace Picard as captain on their sleeves.
 is addressed by all as "Slave" – and worse, he is so inured to this degrading treatment as to be accepting of it (Picard is later shocked to learn that, in the mirror universe, the Klingon Empire was not only defeated in its war with the Terrans, but their entire race was discommended, en masse, and subjugated). 
Picard is most horrified to learn that Beverly Crusher, in addition to being the ship's CMO, is also "captain's woman" (his counterpart's mistress); Picard arranged Jack Crusher's "accidental" death, then likewise arranged a career-ending embarrassment for Beverly that was only averted through his intervention – blackmailing her into his bed. After so many years with him, she is a broken and bitter woman, too numbed to his cruelty to even object to the torturing of her own son.

Picard gleans that the ISS Enterprise is waiting for an opportunity to pounce on its "primary universe" counterpart. On an "inspection" tour of engineering, Picard realizes that the Imperials' plan is to capture the vessel intact, then massacre its crew and return it to the primary universe, masquerading as their counterparts. After a few months of gathering all necessary intelligence on Starfleet's dispositions and defenses, the Empire will invade, challenging the Federation, Klingons, and Romulans on multiple fronts – the mirror universe Starfleet projects that they may be able to conquer the entire quadrant in as little as a year.

While La Forge and Troi continue their attempts to penetrate the Imperial vessel's computers, Picard decides he needs to slow them down with a little sabotage of his own. He takes a handful of surgical nanites borrowed from Beverly Crusher, reprograms them with sabotage instructions, and slips them into the ship's systems. Within an hour, its systems are crashing, leaving it dead in the water. Troi and Picard also incapacitate La Forge's counterpart, and Picard orders "La Forge" to get to work repairing the ship, allowing La Forge to access the computers.

Unfortunately, La Forge is betrayed by one of his assistants, and tortured by Security Officer Troi in the agony booth, where he breaks just enough to allow Troi to realize who "Picard" really is.

Picard rushes to his counterpart's cabin just as the other Picard is regaining consciousness. The two fight, and Picard-prime knocks mirror-Picard out just as Troi's guards storm into the room, killing Barclay in the process. Picard is so enraged at this senseless murder that he forgets his cover and vents that rage full-bore at Troi – an emotional overload that shocks her. Mistaking the unconscious mirror-Picard for the primary universe imposter, Troi weakly orders him taken to the booth, then quickly retreats.

During the confrontation with Troi, Picard is discomfited to realize that that universe's Worf has realized who he really is. Worf does not speak up, however, and he says he will help Picard and his crew escape – a small return for the momentary kindness Picard showed him while acting as the ship's captain.

Troi, acting as her counterpart, has La Forge released from the torture chambers, and they rendezvous with Picard. Before they flee the Imperial ship, Picard repeats the advice given by James T. Kirk to  a hundred years earlier: that the Empire's eventual collapse is inevitable, and now, with the Empire grasping at straws to find "new worlds to conquer", that collapse is closer than ever. Picard urges Worf to spread the word in secret among his people, and the Empire's other subjects, to be ready to rise up when the moment presents itself. Worf, presented with the first ray of hope he has ever known in his life, thanks them and wishes them well. Troi stuns him to cover up his complicity, and all three of them beam back to their shuttle craft, and from there back to the Enterprise.

With the information stolen by La Forge, the Enterprise crew is able to duplicate the "switchback" device the Imperials used, which allows them not only to return to their own universe, but to "snap back" the ISS Enterprise when it tries to follow them.

During the debriefing, La Forge reports that, in escaping from the Imperials, they have perfected a "snap back" method that can be widely distributed throughout the Federation, to repel any Imperial vessels that try to slip through or invade in other parts of the galaxy – the Imperials were so enamored of their new technology that they decided to use it before developing a countermeasure to the "snap back" technique.

Relieved to be "home" at last, the crew releases much of its pent-up tension with an impromptu opera performance in one of the ship's holodecks. After a thoroughly enjoyable evening, Picard leaves with Crusher on his arm, as he reflects that the mirror universe, however morally inverted it was, still had decent people like Worf inhabiting it, and he wonders aloud whether a man really can change the future with just a few words. Crusher kisses him goodnight and says that, in their universe at least, the single word "engage" seems to work wonders.

 Background information 
 Dark Mirror reached number fourteen on the New York Times Best Seller List for , its only week on the list. 
 The Science Fiction Book Club released a special edition of the hardback in .
 Since the novel was written and published prior to  (although the paperback release came after), it appears to contradict the history and development of the mirror universe as seen in , in which the Terran Empire had been conquered by the Klingon-Cardassian Alliance in the late 23rd century.
 The bridge of the ISS Enterprise-D seems to have been influenced by the battleship Enterprises bridge in .
 Different versions of the  and the  later appear on screen in Deep Space Nine.

 Cover gallery 

 Characters 
 Main characters 
 Jean-Luc Picard
 William T. Riker
 Data  Data was programmed with the Delphine language (with an Eastern intonation, as note by Hwiii). An analog of Data does not appear aboard the ISS Enterprise-D, as his creator was killed as a result of political purges in the mirror universe.
 Beverly Crusher
 Deanna Troi
 Geordi La Forge
 Wesley Crusher
 Miles O'Brien
 Reginald Barclay
 Worf
 Keiko O'Brien

 Original characters 
 Hwiii ih'iie-uUlak!ha' Addressed as "Hwiii" for short. A Delphine commander, native of Triton Two, essentially a sapient dolphin. A member of the Starfleet navigation research team, Hwiii is a graduate of Harvard and La Sorbonne, and an expert in hyperstrings. Hwiii had been on sabbatical researching so-called "clean" hyperstrings near the galactic rim when the Enterprise arrived for its patrol. After the initial "switch", Hwiii immediately recognized that a dimensional transfer had taken place, causing him significant distress. Hwiii worked with Geordi La Forge and the Enterprise engineering staff to construct a replica of the ISS Enterprise switchback device, in order to return to the primary universe. He also derived the plan to send the Imperial vessel back to its home universe and prevent a further incursion/capture.

Hwiii navigates through the ship in a force field containing water to allow him to breathe outside of his specially-designed flooded guest quarters, and an antigravity unit that allows him to "swim" through the air, as well as a machine translator to make it easier to communicate with the crew. 

 The Laihe
 Lalairu leader. She warned the Enterprise of local hyperstring disturbances just prior to the "switch".
 Mark Stewart USS Enterprise-D ensign, whose security clearance was used by his mirror duplicate. After the mirror Stewart is apprehended, Worf suggests sending Stewart back to the other Enterprise in his place, but Picard rejects the idea as the risk to Stewart is too great.
 Eileen Hessan
 Mann
 Enterprise security lieutenant who operated the tactical console on the bridge.
 Wooldridge
 Enterprise ensign who reports Hwiii's loud cries to Riker.
 Brendan Ryder
 Security crewman, described as slim. He helped apprehend the mirror Stewart. Crusher asked him how his arm injury was healing.
 Mirish
 Security crewman, described as dark.
 Detaith
 Security crewman, described as blue.

 K!eeei
 Delphine poem performer. His or her works were sources for the Delphine course on cetacean epic poetry.
 Bob Rawlings
 Kowalski
 Gaulgo
 Nassainen
 Ramirez

 Mirror universe 
 Jean-Luc Picard Captain of the ISS Enterprise-D, assumed command on stardate 41124.

 William T. Riker Executive officer of the ISS Enterprise-D.

 Beverly Crusher CMO of the ISS Enterprise-D, and captain's woman to Jean-Luc Picard, after he arranged the death of her husband, Jack.
 Deanna Troi the ruthless security officer on the ISS Enterprise-D, similar to the 'political officers' of the ancient Soviet Navy on Earth.

 Geordi La Forge Chief engineer of the ISS Enterprise-D.

 Wesley Crusher attempts to murder Picard, whom Wesley believes is the mirror version, in revenge for his father's death. As a result, is arrested and placed in the agony booth as punishment.

 Reginald Barclay Picard's personal bodyguard.

 
 Mark Stewart ISS Enterprise-D crewman forced to infiltrate the USS Enterprise-D. After transferring vital tactical data to the Imperial vessel, and being captured by Enterprise security personnel, Stewart dies from a time-delayed viral "bomb" placed in his system by the mirror-Crusher.
 Eileen Hessan
 Brendan Ryder (mirror)
 Security crewman, like his duplicate. Successfully foils the mirror Wesley's assassination attempt on Picard.

 History of the mirror universe Note: Dark Mirror was the first novel to be written as a sequel to , and so its continuity is not consistent with the canon portrayals of the universe, as depicted in episodes of the later series (such as ), or with subsequent mirror universe novels.

 The Terran Empire 
The Terran Empire (called "United Empire of Planets" here) was formed from the ashes of the Eugenics Wars, where Khan Noonien Singh and his Augment followers were not defeated as in the primary universe, but instead established competing empires that eventually wiped each other out in nuclear holocaust, using atomic weapons delivered by ion-powered craft. 

The surviving governments eventually banded together to form the Empire of Earth, and began expanding into space, fixated on assuring the survival of their own race rather than peaceful exploration. In the mirror universe, there was no World War III, a cataclysmic event that convinced the primary universe's Earth population to band together for peaceful purposes.

However, Jean-Luc Picard, examining his counterpart's collection of literature, finds evidence that the "moral inversion" which differentiates this universe was not born out of any single turning point or event, but rather built up gradually over thousands of years, beginning some time around that of the Ancient Greeks (Picard notes that Homer's Iliad is roughly similar to the version he is familiar with, but after that the moral inversion follows swiftly).

After terraforming Mars with a casual indifference (wiping out numerous artifacts and fossils in the process), the Terrans then, with the development of warp drive, expanded out into interstellar space, solely intent on conquest. Alpha Centauri – already inhabited by colonists from another local system – was "cleansed" and re-colonized, as was its foster planet, Gamma Centauri. , having never been grown past its violent roots through the teachings of Surak, became a valued ally of the Terrans.

Eventually, contact was made with the Romulans, leading to a war every bit as bloody as it was in the primary universe. After the Romulans were defeated at the Battle of Cheron, the Terrans invaded the Empire itself, destroyed Remus, and demanded the surrender of Romulus. The Romulan people committed collective suicide rather than surrender, and the Empire took over the planet. Not long after, the United Empire of Planets was formed, and continued to expand. 

As narrated by Worf's counterpart, when the Terran and Klingon Empires clashed, the Terrans were eventually victorious, after another protracted and bloody conflict. Unlike the Romulans, the Klingons chose to live, and the Terrans discommendated them, en masse, and reduced them to serve as slaves.

Jean-Luc Picard remarks on the irony that the mirror universe's inhabitants have never encountered Q or the Borg, the only powers he can think of that might actually have outmatched and humbled them.

By the late 24th century, the Empire encompasses the entirety of the galaxy's Sagittarius Arm.  Because the Sagittarius arm has become disconnected from the rest of that universe's Milky Way galaxy by everything but gravity, they have run out of viable systems to conquer. Now, there are no inhabitable worlds beyond the Empire's borders that can be reached in less than ten to twenty years, even at high warp speeds – hence the impetus to find a way to invade the primary universe.

 Aftermath of  
 did more than "consider" Kirk's parting message. With the use of Kirk's Tantalus field, he became a powerful and influential figure in Starfleet Command and attempted to reform the Empire from within, but was ultimately unsuccessful. He was framed on treason charges and executed, some twelve years after the original "crossover" incident. His father, Sarek, was likewise assassinated a short time later.

Before escaping the ISS Enterprise-D, Picard tells Worf's counterpart that Spock had predicted the Empire would collapse in approximately two hundred years; in their time, one hundred of those years had already passed, and the Empire was closer to collapse than even Spock anticipated. Picard encouraged Worf to spread the word among his people, to be ready to rise and retake their freedom and their honor when the chance came.

 The ISS Enterprise and its operational history 
In the mirror universe, the ISS Enterprise (ICC-1701-D) is similar in appearance to its  counterpart, but displays marked differences: 
a more threatening "gun-metal gray" hull color;
a deeper curve to the primary hull; and
a larger secondary hull with warp nacelles raked further forward.

In summary, Picard finds it "a cruel look, and intimidating" (p. 62). 

The Imperial ship's engine power and weaponry is also significantly greater: more powerful phaser banks, a complement of photon torpedoes six times greater than the USS Enterprise carries; more powerful deflector shields, and several different varieties of weapons not equipped on Federation vessels: "nova devices", "molecular disassociators" (described as an improvement on a weapon first developed by the Romulans, possibly an early variant of the disruptor), and "atomics in several different flavors."  The reason for the last item on the list is not given, but the Empire may have decided that the relatively low power of these weapons was an acceptable loss given that, unlike photon torpedoes, they wouldn't compete with the engines for antimatter.

It is only notably inferior to its counterpart in terms of sensor capability, Worf reflecting that, like the Klingon warriors of old, they have focused so heavily on offensive capability that their ship's ability to observe in secret is notably hampered, allowing USS Enterprise to briefly monitor ISS Enterprise without them knowing.

Similar to Kirk aboard the mirror Enterprise, Jean-Luc Picard asks for an operational history of his counterpart, and is revolted to hear an "inverted" version of the Enterprises early missions (as chronicled in the first season of TNG):
Picard assumed command after the destruction of his previous command, ISS Stargazer (ICC-2055) at the Battle of Maxia.
The destruction of Farpoint Station during the attack by an alien entity ();
The irradiation of an entire continent of Ligon II (killing an estimated thirty million people), when its inhabitants refused to surrender the vaccine needed to treat the outbreak of Anchilles fever on Styris IV ();
The recovery of a stolen T-9 energy converter from the Ferengi, followed by the genocide of the Ferengi race through the "prejudicial" terraforming of their world ();
The destruction of the Tarellian starship menacing Haven ();
The destruction of the entity overseeing the Edo species on Rubicun III, then incorporating the Edo into the Empire ();
The destruction of the Jaradan species ();
The decimation of the Aldeans as punishment for trying to kidnap imperial children to repopulate their dying race (); and
The destruction of the crystalline life form on Velara III to allow that planet's terraforming to continue ().

 References Lalairu: A culture comprised of nomadic space-faring species which roam the fringes of the galaxy. Also known for their erratic linguistic conglomerate.Alexander the Great: King of ancient Macedon and famous military leader; in reviewing the state of the Empire's conquests, and how it has been "quarantined" by the surrounding empty space, Picard echoes the quote "no more worlds to conquer" often attributed to, or made about, Alexander. and James Joyce: 20th century Earth novelists. Picard wishes Burgess and Joyce had assisted in programming translations of Lalairu communications, feeling that they may have been among the few authors whose own writing was erratic enough to make Lalairu comprehensible to them.William Shakespeare: Medieval English playwright. Picard is horrified to trace the moral inversion in several of his mirror universe counterpart's plays, including:
: In which Portia successfully argues that Shylock has the same right to justice as any man, that his "pound of flesh" could never be received without blood being spilled. "The quality of mercy must be earned", she extols, and Antonio is killed as a result. In addition, Lorenzo betrays Jessica, who commits suicide using his sword.

, , and  are largely identical to their primary universe versions, except that one of the few humane references in Lear – stage directions depicting Gloucester's servant trying to prevent his master's execution – is absent.: 19th century Earth novelist. Picard notes that Kipling, "idiosyncratic as always," is one of the few authors whose "mirror" work is largely unchanged.Aristotle: Ancient Greek philosopher. Picard notes that Aristotle's work is largely unchanged, being one of the rare humane voices.Plato: Ancient Greek philosopher. Unlike Aristotle, in the mirror universe Plato's work is completely inverse to his primary universe counterpart's – he now argues that the most effective government is government by the strong for the protection of the weak, maintained through fear (similar to ).Homer: Ancient Greek epic poet. Picard finds that Homer's epic poem Iliad is mostly the same as its primary version, indicating that the moral inversion began after it was written; however, small traces of ruthlessness can still be found in the text – in the scene when King  of Troy begs  to release his son, 's body for burial, Achilles murders Priam in cold blood.: 15th century French poet. Picard finds himself repeating Villon's poetry in his head to confuse the mirror-universe Troi, who scornfully dismisses the poetry as "third-rate."Transilience: a theoretical method of space travel, enabling instantaneous transportation over several thousand light years (a method that seems to have been perfected by the Iconians). Picard reflects that transilience is the only solution he can think of to traverse the vast swathes of empty space surrounding the Empire, and it is still so far from becoming reality that the Empire will not achieve it before its collapse.Zefram Cochrane (misspelled "Zephram Cochrane" in the novel): the inventor of warp drive in both universes; in the mirror universe, his invention fueled the Empire's first serious expansion.Dreadnought: A class of starship in the primary universe that Riker suggests is their closest analogue to the ISS Enterprise''-D.
Fifth House of Betazed: The family to which Deanna Troi and her mother, Lwaxana belong; Deanna finds herself imitating her mother's imperious manner as a "Daughter of the Fifth House" while trying to play her role as her mirror universe self.
Picard Maneuver: When wearing his counterpart's Imperial uniform, Picard attempts to tug down the front, only to find that he can't; he is irritated to find that the mirror universe's designers have somehow fixed the problem that his own uniforms always have.

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