A Mondasian colony ship was travelling from Mondas to pick up colonists. When the ship almost traversed into a black hole, the crew experienced the effects of time dilation, where time on the lowest decks of the ship was travelling faster than on the upper decks.
The ship was approximately 400 miles long and around 100 miles wide.
The ship contained over a thousand decks, each of which presented a Mondasian environment. These included:
- 0000 - The main control deck. (TV: World Enough and Time)
- 0502 - A deck containing a solar farm. (TV: The Doctor Falls)
- 0507 - A deck containing the largest of the ship's solar farms. (TV: World Enough and Time) The locals here were saved by the Twelfth Doctor, Bill and Nardole. (TV: The Doctor Falls)
- 0900 - A city deck. More evolved Cybermen were invading here. (TV: The Doctor Falls)
- 1056 - An urban deck, containing various apartment blocks and a hospital. (TV: World Enough and Time) Eventually turned into a Cyber-factory. (TV: The Doctor Falls)
- Other floors mentioned on the lift scanner are: 1052 to 1015, 0951 to 0884, 0737 to 0679, 0668 to 0643, 0493 to 0472, 0031 to 0027, and 0010 to 0007. (TV: World Enough and Time)
- Further floors mentioned on the lift level indicator at floor 0507 are: 0797 to 0738, 0509 and 0508. (TV: The Doctor Falls)
At take off, there were fifty crew members aboard the ship. They included Jorj: a member of janitorial staff. Following the effects of time dilation, the ship became filled with generations of lifeforms, each descended from the ship's crew.
The ship was fitted with super-fast inertia lifts and was propelled by rear thrusters. Aboard the lowest decks, evolution of technology was advanced. In order to adapt to expiring environments, an artificial evolution was devised. The Mondasian inhabitants were gradually upgraded into Cybermen. (TV: World Enough and Time)
The colony ship was commissioned to transfer inhabitants of Mondas, for which it was headed with a skeleton crew of 50, including the janitor Jorj. En route, it was drawn into the gravity well of a black hole. The crew sent a team of 20 to the lowermost level, floor 1056, to reverse the engines and pull the ship free. However, time dilation caused by the black hole's gravity resulted in time passing much more slowly at the upper parts of the ship, which were closest to the black hole.
Due to time dilation, the team at the bottom of the ship found that they experienced over 500 years for every day that passed on floor 0000. Thus, after reversing the engines, they and many generations of their descendants lived out their lives on floor 1056. They built an industrial civilisation, but eventually they began to run out of resources and their environment became irreversibly polluted. At one point, an expedition was sent to floor 0507 to explore the possibility of moving there, but again due to time dilation they were never heard back from again.
At some point, the Master, after being banished from Gallifrey, landed on floor 1056. The Master's attempt to escape the black hole by going too fast burned out his TARDIS' dematerialisation circuit and stranded the Master on the colony ship. The Master "killed a lot of people, took over the city, lived like a king" before the people of floor 1056 tired of his cruelty and overthrew him. The Master was forced into hiding as "Mr. Razor", the caretaker of the hospital.
Eventually, the people of floor 1056 were forced to convert themselves into cybernetic humanoids to survive. The prototypes would venture to the upper floors to take the rest of the crew members for conversion, leaving only Jorj as he wasn't completely human.
On Floor 0507, there resided a group of farmers who possessed rifles. They were faced by the prototypes that had travelled to their floor from 1056. They spent the night shooting them down, then stringing them up on wooden crosses during the day. They were plagued by these "cyber scarecrows" (as one child called them) for an unknown amount of time - they had left floor 1056 for several hundred from their perspective. One day, a shuttle raft blasted through the floor, containing the Doctor, a cyber converted Bill Potts, the Master, Missy and Nardole. With the Doctor injured, Nardole rallied the town over the coming weeks to prepare for a Cyberman invasion; the prototypes were merely the advance guard. As such, the siege of floor 0507 began. Nardole hacked the floor to ignite certain fuel lines around the floor to fool the Cybermen their technology was a threat to the Cybermen. Floor 507 was ultimately destroyed by the Doctor along with most of the Cybermen. Nardole moved the townspeople to floor 502 where there was another solar farm and they would be safe for years until the surviving Cybermen could regroup and find them.
During the siege of floor 507, Missy provided the Master with a new dematerialistation circuit for his TARDIS, allowing him to depart the colony ship. However, before he left, Missy forced a regeneration upon the Master and the Master killed Missy with his laser screwdriver.
The Doctor also stayed behind on floor 507 to delay the invading Cybermen while Nardole evacuated the townspeople, using the sonic screwdriver to detonate more fuel lines until he was eventually shot down by the Cybermen, beginning his own regeneration. Before the process could take hold, he used the sonic screwdriver to detonate the entire floor, destroying the majority of the Cybermen. (TV: The Doctor Falls)