The Crustacoids were a crustacean race.
A group of Crustacoids, believing they had a divine right to rule, attempted to conquer the universe. The Time Lords incarcerated them in a prison in the 1930s Sussex countryside which resembled an English manor house and was guarded by robots. They made the Crustacoids believe that they were still fighting the war, that the prison was a fortress and the guards their servants. Eventually, the prisoners all killed each other.
In 1933, some time later, the Second Doctor, Jamie McCrimmon and Zoe Heriot arrived at the house, where they were attacked by the robots. The Doctor escaped and, with the help of Lucas Seyton, freed his friends. (PROSE: Fallen Angel)