Deep space, four days from Earth, 1981. The TARDIS materialises aboard a massive Urbankan starship. What is the real agenda of Monarch, master of the vessel?

The Doctor and his companions explore Monarch's vessel. But what is the secret of the ancient Earthlings aboard?

Bigon reveals Monarch's terrible plan to the Doctor. Can he act in time to save Nyssa? And which side is Adric on?

The Doctor has little time left to stop the evil Monarch. But he is losing allies — and the TARDIS is gone.