This free download is the first episode from Doctor Who: The Sixth Doctor Adventures: Water Worlds.
The Sixth Doctor returns, and he's thrown straight in at the deep end! Travelling the galaxy with Melanie Bush and their brand-new companion, marine biologist Hebe Harrison, there are wonders to see, dangers to face and plenty of peril beneath the waves.
1.1 The Rotting Deep by Jacqueline Rayner
A mysterious SOS summons the Doctor and Mel to an oil rig in the North Sea where a dwindling group of survivors awaits rescue from a lethal menace. One of their number is Hebe Harrison, a wheelchair-using marine biologist who is definitely more than she seems. Can our heroes escape the rig? And just what is killing off the rig's beleaguered crew?