Another adventure for everyone's favourite time-traveller. The Doctor (Tom Baker), Romana and K9 find themselves suspected of being drug smugglers when they arrive on the Empress, a luxury liner. The Empress has become merged with another craft, the Hecate, after colliding during a hyperspace jump. Somebody on board the Empress is smuggling Vraxoin, a deadly addictive drug, and matters are complicated still further when the Mandrells, a race of monsters being transported from the planet Eden, are let loose on board the ship.