Two spaceships have a hyperspace collision and become locked together causing the area where they are connected to become unstable due to the intersection of the hyperspace fields. The Doctor and Romana arrive and become involved. The Doctor discovers a crewman using the dangerous drug Vraxoin.

While being chased by the customs officials as smugglers, the  Doctor and Romana work to both track down the smuggler and to separate the two ships. During all this excitement, multiple Mandrels have escaped from the CET machine and the Doctor discovers their secret.