The Doctor and Romana arrive on a space liner orbiting the planet Azure, which has just been impaled by a private spacecraft due to an accident leaving hyperspace. The accident happened because the navigator of the liner was stoned out of his mind on a horribly addictive illegal drug called vraxoin, and it appears somebody onboard the liner is smuggling it. The Doctor and Romana are further endangered when the brutal and stupid local border guards assume that the Doctor is a drug-dealer because he was carrying some vraxoin he discovered around as evidence.