Floor 0507, or more simply Floor 507, was a floor on a Mondasian colony ship. Serving as the largest of the ship's solar farms, it became the location of the final battle between its Mondasian inhabitants and an army of Cybermen from Floor 1056 that were determined to convert the Mondasians and complete Operation Exodus. Following the Mondasians' evacuation to Floor 0502, the Twelfth Doctor ignited all the fuel underneath Floor 0507, destroying the Cybermen at the cost of his near-death and the incineration of the entire solar farm.
Landscape and technology
As the largest solar farm on the entire Mondasian colony ship, Floor 0507 resembled a large, spring countryside commonly found on Earth. It featured a large farmhouse, which served as the home of several dozen Mondasian adults and children, such as Hazran and Alit, following the arrival of the patients, who the adults fought off with rifles. Additionally, a sealed service duct could be accessed through the farmhouse's cellar. Other buildings on Floor 0507 included a barn near the farmhouse which Bill Potts slept in after she arrived on the solar farm, (TV: The Doctor Falls) and a horse stable a few days' worth of travel away from the farmhouse; this stable featured a cargo lift that travelled between Floor 0507 and Floor 0508. (PROSE: Alit in Underland) A windmill was located near the farmhouse before Nardole destroyed it.
Despite its appearance, Floor 0507 contained advanced technology. Underneath the soil of the floor was a large network of fuel lines and fusion turbos, which Nardole hacked into via a laptop. Floor 0507's sky was holographic, with the floor's number visible on its ceiling. Like every floor on the colony ship, Floor 0507 was connected to the other floors via inertia lift - located in a large forest - for quick travel between floors, although the time dilation caused by the black hole near the ship significantly delayed such travel. (TV: The Doctor Falls) The superstructure walkways underneath Floor 0507 featured terminals and holo-emitters designed to maintain the solar farm. (PROSE: Alit in Underland)
Following the Twelfth Doctor's act of igniting all the fuel underneath Floor 0507 after the Mondasians' evacuation to Floor 0502, Floor 0507 resembled an incinerated wasteland, littered with dead, scorched trees and the remains of hundreds of destroyed Cybermen. (TV: The Doctor Falls)
When the Mondasian colony ship almost flew into a black hole, it was affected by time dilation. (TV: World Enough and Time) As it was located close to the middle of the ship, time on Floor 0507 moved faster than on the upper floors, such as Floor 0000, but slower than the lower floors, such as Floor 1056. (TV: The Doctor Falls) A number of carters transported food and grain produced on Floor 0508 to Floor 0507, along with several of the ship's upper floors, but Alit later noted that as she grew older, the carters travelled to Floor 0507 on a less frequent basis. (PROSE: Alit in Underland)
Attack of the Cybermen
When the Mondasians of Floor 1056 began evolving into Cybermen as part of Operation Exodus, a patrol of patients was sent to Floor 0507 to capture its Mondasian population for cyber-conversion. However, the patrol never returned to Floor 1056, as the patients were shot down by the adult farmers at night before being chained to crucifixes in the fields during the day. However, the patients would break free at night and resume their original mission, forcing the Mondasians to constantly fight off the patients at night and enchain them again in the day. (TV: The Doctor Falls) For her own protection, Alit was sent by her parents to live in a large farmhouse on Floor 0507 with the adult farmers and the other children. (PROSE: Alit in Underland)
The Doctor's arrival and the CyberNeomorphs
The day after another patient attack, Alit observed a shuttlecraft crash-land on Floor 0507. She encountered its crew - Nardole, the Master, Missy, and a cyber-converted Bill Potts carrying an unconscious Twelfth Doctor - who had escaped from Floor 1056 after its Mondasian inhabitants had evolved into Mondasian Cybermen and attempted to kill them. (TV: The Doctor Falls) After the group reached the farmhouse, the Master lied to Nardole and Hazran about their intent to travel to Floor 0508 to stop the patients and find a means of escaping the ship, secretly intending to find a means of regaining control of the Cybermen. When he left with Missy that night, Alit followed them to the crashed shuttle; after encountering a patient, Alit joined the Master and Missy on their expedition. Together, on Floor 0508, the group eventually destroyed a patrol of CyberNeomorphs who attempted to attack Floor 0507 with a swarm of Cybermats so as to weaken its Mondasian inhabitants in preparation for a future invasion. Following this, the Master, Missy and Alit returned to the farmhouse on Floor 0507 on a horse-and-cart. (PROSE: Alit in Underland)
The Doctor's final stand
Two weeks later, Nardole assisted Hazran in helping the farmers prepare for battle against the Cybermen. Bill had spent the fortnight sleeping in a barn to avoid scaring the children, and by this point, the Doctor had mostly recovered, and attempted to comfort Bill after her cyber-conversion. The duo followed the Master to Missy after they located Floor 0507's lifts in a nearby forest; after Missy called one of the lifts, the four destroyed a highly-evolved Cyberman in the lift, and quickly returned to the farmhouse as the Cybermen sounded an alarm and began flying en masse to Floor 0507. As the Doctor and Bill accessed a service duct in the farmhouse's cellar, Nardole hacked into the fuel lines underneath Floor 0507, allowing him to ignite the fuel to trigger remote explosions as a means of fighting the Cybermen. Meanwhile, the Master and Missy discussed a plan to travel to Floor 1056 and escape in the Master's TARDIS; that night, just after the Cybermen arrived, the Doctor attempted to stop them leaving, but failed.
The initial wave of Cybermen attempted to capture the Mondasians of Floor 0507 for conversion, but were fought off by the farmers and Nardole attacking in conjunction, prompting the Cybermen to briefly retreat and prepare for a second assault to kill the Mondasians instead. The Doctor used this brief window of time to order Nardole and Hazran to lead an evacuation of the children through the service duct in the farmhouse's cellar to Floor 0502 via the lifts. Bill chose to stay behind with the Doctor to destroy the Cybermen after the children's evacuation.
Meanwhile, Missy and the Master reached the lifts, and Missy stabbed the Master before he returned to his TARDIS on Floor 1056, allowing him to escape before regenerating into Missy; before doing so, the Master attempted to permanently kill Missy with his laser screwdriver, (TV: The Doctor Falls) but Missy used an Elysian field to regenerate into the Lumiat before escaping as well. (AUDIO: The Lumiat)
During the Cybermen's second assault, the Doctor, after being struck down by a Mondasian Cyberman in the forest, ignited all the remaining fuel underneath Floor 0507, destroying the Cybermen and reducing the floor to an incinerated wasteland. Bill barely survived, and was transformed into a creature of sentient oil by Heather, who found Bill through Heather's tears. Together, Bill and Heather left Floor 0507 with the Doctor's severely-wounded body. (TV: The Doctor Falls)
Behind the scenes
This number has made it into RTD-era scripts, including TV: Boom Town, Army of Ghosts, The Shakespeare Code, 42, Voyage of the Damned and The Poison Sky. Death of the Doctor, a script penned by Davies for The Sarah Jane Adventures, has the Eleventh Doctor claim he has 507 regenerations.