The Doctor, Romana and K-9 find themselves on the planet Alzarius, whose colonists are besieged by reptilian creatures rising from the marshes. Trapped in E-Space, the Doctor, Romana and K-9 are unaware that Adric has stowed away aboard the TARDIS. Their next stop brings them face to face with a hideous creature from Time Lord legends. Still lost in E-Space, the TARDIS is hijacked by the time-sensitive creature and brought to a crumbling ruin in a lonely white void, where another ship is stranded and in trouble.