Doctor Who: The Brood of Erys (183)

Space travellers are warned to keep away from the area of the planet Asphya and its unremarkable moon Erys. Not the best place to materialise the TARDIS, then - as the Doctor discovers when his ship is raided by the imp-like Drachee, and his companion Flip is carried away...

But the TARDIS isn't the only stricken vessel in the region. Aboard a nearby space yacht, the Doctor encounters a woman who holds in her head the secret of Erys - a secret suppressed by amnesia, or worse.

Flip, too, is about to learn Erys' secret. But once you know Erys' secret, you can never escape.