Battle at Federation Headquarters
The Battle at Federation Headquarters was a conflict fought between the United Federation of Planets and the Emerald Chain in 3189, after forced peace negotiations between the Federation and the Chain broke down. ()

Prelude
A few days before the battle, the USS Discovery was on assignment at the Verubin Nebula, investigating the burn and  a Federation distress call coming from somewhere within the nebula. While there, the ship and its crew were attacked and captured by Osyraa. Her ship, the Viridian, latched onto Discovery, and used the ship's Spore Drive to jump them both back to Federation Headquarters. ()

Once there, Osyraa opened forced negotiations with the Federation, however, she broke up the talks when Admiral Charles Vance said the only way the Federation would accept the alliance was if Osyraa faced justice for her crimes. Osyraa refused and returned to Discovery, where she discovered that the senior staff, thanks to the Andorian Ryn disabling the sensors, were attempting to retake control of Discovery. She demanded Ryn to restore the sensors. Ryn refused and Ossyra killed him. She then ordered the Viridian to open fire on Federation Headquarters so they could escape. ()

The battle
As Discovery attempted to escape the shield of Federation Headquarters, Admiral Vance ordered the  to take the lead on Viridian, while the rest of the fleet inside the shield targeted the Discovery. Aboard Discovery, Osyraa ordered her regulators to fire on the complex's primary shield emitter, which was disguised as a secondary deflector array. Lt. Audrey Willa told Vance the emitter would last less than five minutes against the barrage and Vance ordered the fleet to hit Discovery harder.

As Discovery left the shield perimeter, a regulator reported that Discoverys crew was engaged in a firefight on Deck 7. Osyraa ordered all regulators to evacuate to Deck 5 or above immediately.

On Deck 7, Sylvia Tilly, Gen Rhys, Joann Owosekun, Keyla Detmer, R.A. Bryce, Lt. Ina, and DOT-23 drones controlled by the Sphere data traded fire with the regulators, who retreated to the upper decks per Osyraa's instructions. The computer reported life support was being shut off and atmosphere drained.

The complex's shields started to fail, allowing the Viridian to provide cover fire for Discovery to escape. A surprised Lt. Teemo reported that a Ni'Var fleet was about to arrive to provide backup. The Ni'Var s were blocking Discoverys path out, so Osyraa directed the Viridian to deploy its cache of pesticides, targeting shuttlebays, airlocks, and other intakes. Before that could occur, Michael Burnham contacted Vance, asking him to stand down. Regardless, Discovery was still being pursued by the Federation and Ni'Var fleets.

In engineering, Tilly and the other officers were having difficulty breathing and are sharing one oxygen mask among them. Owosekun explained that she had superior lung capacity having grown up free-diving for abalone in the Ogbunike Caves. Bryce reported he could not bypass the Emerald Chain's command functions. A hard reboot could restore computer systems, but they would have to access the data core. Burnham and Booker, grounded by the transporter jammer, snuck through the ship, avoiding regulators. Using one of the regulator's badges, Burnham broadcast an audio message across the ship: "It wasn't a particularly happy birthday. But I found you. We played seven-card stud and drank synthehol. Too bad we didn't have fireworks. Nothing stops a party like fireworks." Tilly explained to the others that on her birthday the year prior, she was going "through a hard time" and hid in a nacelle after her shift. Burnham found and distracted her until midnight, never mentioning Tilly's birthday. Tilly realized Burnham's message was directing her to use an incendiary device to destabilize the superconductors holding the now-detached nacelle in place, knocking the ship out of warp and allowing the pursuing fleets to catch up.

Owosekun arrived at the nacelle access point having run out of supplemental oxygen and barely able to stand. She placed the bomb but collapsed before leaving. One of the DOT-23 drones controlled by the Sphere data arrived, urging her to stand. It reached out for her just as the bomb exploded. The nacelle now destabilized, Discovery was forced out of warp. Discovery reentered normal space, careening wildly off its axis. The turbulence knocked Burnham and Booker, as well as their respective assailants, to the ground. The Viridian surrounded Discovery inside a large internal chamber to protect the ship from the pursuing force.

In the data core, Osyraa and Burnham engaged in hand-to-hand combat, and Osyraa managed to force Burnham into a wall made of programmable matter. Burnham pointed out that they did not have to be enemies, but Osyraa responded that trying to negotiate with Vance was a mistake. She pushed Burnham backwards into the wall, which subsumed her. Osyraa looked on satisfied, but a few moments later Burnham shot from inside the wall before emerging and coughing up some of the matter. Burnham performed a hard restart of the computer systems, restoring the Starfleet programs. Having regained control, she restored life support on all decks, beamed the regulators off Discovery and diverted auxiliary power to shields. On a shipwide channel, she ordered any crew who can hear her to report to the bridge.

On the bridge, Michael proposed a plan to overload and eject the ship's warp core and jump from inside the Viridian using Booker to control the Spore Drive. They enacted the plan, and Discovery managed to jump away seconds before the warp core detonated, destroying the Viridian from the inside. ()

Aftermath
After regaining control of their ship, Discovery successfully returned to Theta Zeta and retrieved Captains Saru, Dr. Culber, Adira Tal, and Su'Kal. Discovery returned to Federation Headquarters. For her actions in recovering the ship, Michael was promoted to Captain, and took command of Discovery. Discovery was ordered to rendezvous with the Coloma at Theta Zeta, pick up dilithium and deliver it to two Federation worlds, five non-federation worlds, and a starbase. 

Without Minister Osyraa's command, the Emerald Chain fractured, and was no longer a threat to the Federation. 

President T'Rina returned to Federation Headquarters to officially open a dialog to rejoin the Federation. ()

External link 
 
Federation Headquarters, Battle at