Horror of Fang Rock, Part Three

Résumé :

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.