Doctor Who - Season 21 Episode 25
The Twin Dilemma (3)

The Doctor arrives on Jaconda, once lush and green, to find it completely devastated by giant gastropods. Old legends about the planets half-human/half-slugs werent just myths after all. With or without help from the Doctor and his unpredictable mood swings, Lt. Lang is up for rescuing the twins, who are finally informed of the grand purpose theyve been brought to Jaconda to accomplish.