 The Doctor is pulled out of his time stream and summoned to a Time lord space station above Gallifrey. On his arrival it is announced by the Inquisitor(Lynda Bellingham) that the Doctor will stand trial. Accused of conduct that is unbecoming a Time lord. The Doctor refutes the allegations made against him and chooses to mount his own defence, rather than entrust his fate to a fellow Time lord. Opposing the Doctor and appearing for the prosecution is the Valeyard(Michael Jayston). An enigmatic figure who is clearly out for the Doctor s . Suffering from short term memory loss as a result being taken out of time and puzzled as to the absence of his companion Peri(Nicola Bryant). The Doctor can only sit back and watch as the Valeyard mounts his case against the eccentric time traveller. The first piece of evidence is taken from the matrix. The repository of all knowledge. It chronicles the Doctor s interference in affairs of the planet Ravalox. A planet, very similar to Earth and which was partly decimated by a fireball several centuries ago. Accompanied by Peri in this adventure. The Doctor and his young friend discover that there is more to the planet than meets the eye. Why do the duo discover what appears to be an old abandoned subway station with an old sign that reads  Marble Arch ? Who are the underground dwellers that live beneath the train station? What are the motivations of the Tribe of the Free who are ruled over by Queen Katryca(Joan Sims)? Why do the two villainous rogues, Glitz(Tony Selby)and Dibber(Glen Murphy)want to destroy the totem to the Frees god? And what is the god like immortal of who the underground dwellers speak of? These questions and other are soon answered as the Doctor soon realizes that he might be the only one capable of saving Ravalox and possibly the whole universe from destruction.