A death scream is heard, yet all are accounted for. Eventually the Doctor finds a body stashed away but hours old, with rigor mortis already settling in, which means there's a chameleon in their midst. Completely cut off from the rest of the world and with an escalating body count, the Doctor wonders just what, exactly, he's locked inside the lighthouse with them all.

"Contact has been made!" A relief crew en route to Titan in 5000 AD unwarily pick up hitchhikers that change them. Shortly thereafter the Doctor, passing through the same point in space, is hitchhiked as well, but not Leela - a reject who must die.