Devil World
Devil World is a Bantam TOS novel, written by Gordon Eklund, first published in .

Summary 
From the original book jacket
VOYAGE TO HEARTLAND

Heartland… a mysterious planet populated by a small but terrifying race of demonic beings.

Heartland… where Captain Kirk falls in love with a beautiful, mysterious woman with a fatal secret.

Heartland… where Kirk, Spock, and the rest of the  crew will be challenged by an awesome disembodied intelligence, more powerful than any other force in the universe!

While on shore leave at Starbase 13, Captain Kirk and his officers meet the renowned senseo-artist Gilla Dupree, a pale and fragile woman desperately seeking her lost father, Jacob Kell. When Kirk learns that Kell was last seen on Heartland, a planet that was quarantined after one hundred colonists went mad, he decides to help Gilla retrieve her father while removing him to enforce the quarantine. The crew of the  discovers that the native inhabitants of Heartland, the demonic-looking Danons, constructed a massive god-like super-computer called the Great Machine to help win an ancient war. 

However, as this ancient race nears extinction, the Great Machine becomes desperate to find someone to take the place of the Danons. Most humanoids go insane when they encounter the machine – Jacob Kell was one of the very few who were strong enough to act as the Great Machine's instrument. Gilla, who is dying from a massive and untreatable tumor, refuses to abandon her father to this fate. She gives her last days to take his place so that he may live. Kirk attempts a rescue but barely escapes with his life. He is forced to recommend a continuation of the quarantine to Starfleet while a woman he loves dies on the planet below him.

Memorable quotes 
"The machine knows about you. It'll never let you go. It needs you too much."
"But why?" said Kirk. "Aren't the Danons enough?  Why should it want us?"
"Because the Danons are dying. What can be lonelier than a god no one worships?"

Background information 
 This was the second Star Trek novel by Gordon Eklund, who had previously written The Starless World.

Cover gallery

Characters 

James T. Kirk  Captain of the , who had a brief affair with Gilla Dupree.
Spock  First officer and science officer of the Enterprise.
Leonard McCoy  Ship's surgeon and Chief Medical Officer of the Enterprise.
Montgomery Scott  Chief Engineer of the Enterprise, in command of the ship during the away mission on Heartland.
Hikaru Sulu  Chief helmsman of the Enterprise, part of the away team to Heartland.
Chekov  Navigator of the Enterprise, part of the away team to Heartland.
Uhura  Chief communications officer of the Enterprise.

Reni Bates  One of the original Terran colonists on Heartland who stayed after the evacuation. He escaped the fate of the rest of the colonists (insanity) by refusing to ever merge with the Great Machine. He was responsible for enlightening Captain Kirk as to the true nature of the "mental force" Spock kept sensing.
Dazi  Lead host and spokesman for the remaining Danons on Heartland.
Doyle  A security guard with the rank of Crewman who was part of the away team to Heartland. He was a compulsive gambler who was raised in the Rigellian system. He attempted to gain "immortality" through merging with the Great Machine, but was driven insane by the experience.
Gilla Dupree  A thirty-something humanoid female, formally of Earth, who was a renowned senseo-artist and the composer of Birth of a Living Star. She sought a reunion with her missing father, Jacob Kell. She stayed behind on Heartland to act as part of the Great Machine, and is presumed to have died shortly after the events of this book due to an advanced and untreatable tumor.
Dr. Faustus  A magician who performed at Starbase 13.
Jacob Kell  A former starship captain who developed severe social anxiety after being adrift in a spacesuit for twenty-seven days. He renounced the Federation and defected to the Klingon Empire in exchange for the promise of a Class M planet where he could live out his life in solitude. The Klingons later reneged on the deal and pressed him into service as an archivist for the Klingon Ministry of Space Exploration. He later settled on the quarantined planet of Heartland, where he became part of the Great Machine. He was rescued by his daughter Gilla Dupree.
Merkle  A trader who discovered Jacob Kell's whereabouts while illegally landing on Heartland and later gave this information to Gilla Dupree.
Mosley  A security guard with the rank of Crewman who was part of the away team to Heartland. A friend of Crewman Doyle.
Albert Scheng  The son of Commodore Wilhelm Scheng, assigned to Starbase 13 after washing out of Starfleet Academy and being demoted to Crewman. He joined the crew of the Enterprise as a personal steward to Captain Kirk on stardate 4231.2, and was later transferred to the security division after saving the life of Captain Kirk on the Heartland away mission.
Wilhelm Scheng  A commodore, and the commander of Starbase 13. He was the father of Albert Scheng, whom he asked Kirk to take on as an improvement project.

References 
Danons  The native inhabitants of Heartland who were facing extinction. Most Danons were barely a meter tall with copper skin, narrow black eyes, two curved horns protruding from the head, and a forked tail. At one point this race controlled half of the galaxy, but a prolonged war with the Torgas forced them to return and remain on their home planet. At the time of the novel, the once thriving civilization had dwindled to only one hundred adult Danons, and no children had been born for at least a century.
Great Machine  A super-computer created by the Danons to achieve victory in an ancient war against the Torgas. The Great Machine contained the life essence of all Danons, and in turn controlled the life of each member of that race. Joining the Great Machine offered a form of immortality, as the life essence would be forever preserved in a type of collective consciousness. As the Danons started to become extinct, the Great Machine attempted to join with non-Danons to ensure survival. Most non-Danons became insane after being exposed to the Great Machine, including almost all of the Federation colonists of Heartland.
Heartland  An M-type planet known to the Federation as NC513-II that was the home to an ancient race known as the Danons. A Federation colony was attempted on this planet around the year 2230, but ended in failure when almost all of the Terran colonists went insane.
Herbarium  A garden on the Enterprise that contained a thousand untamed varieties of Earth-like plant life. The sky was painted blue to resemble that of the Earth.
Senseo-drama  The synthesis of symphonic music and holographic storytelling, which was a fairly new form of artistic expression in the 23rd century.
Torgas  The opponent of the Danons in an ancient war.

External link 
 

de:Der Teufelsplanet
Novels