A mysterious disturbance in the hyperspatial vortex causes the Doctor and Sam to materialise the TARDIS in deep space. Here they find that a huge derelict alien craft has become the subject of a dangerous confrontation between starships from the rival systems of Nimos and Emindar. At the centre of the dispute is a ruthless politician with secrets of his own — a man who is willing to risk innocent lives to claim the derelict for himself.