The Doctor and Guy arrive at an Earth colony after hearing disturbing reports of ships being sunk out at sea by some unearthly force. The Doctor feels the situation needs investigating, and Guy feels the need for a holiday.
The pair of them set off in a hired boat to discover just what is going on - why are boats sinking in calm weather? Why has there been a strange glow sighted in the ocean depths?
Before long, their boat is attacked out at sea - but by whom and why, the Doctor doesn't know. All he does know is that Guy is in danger - and he must find him before whatever is out there is able to claim more lives...
Set between 'The Magical History Tour' and 'Smokescreen', this Short Trip adventure is another in a series of adventures featuring the BTR Ninth Doctor.