Mel and Pex play cat and mouse with the lethal cleaner robots while the Doctor and the surviving Kangs learn all about Kroagnon the Great Architect.
Quest roles:
Clive Merrison(Deputy Chief), Brenda Bruce(Tilda), Richard Briers(Chief Caretaker), Judy Cornwell(Maddy), Elizabeth Spriggs(Maddy), Catherine Cusack(Blue Kang Leader), Simon Coady(Video Commentary (voice))