Doctor Who: Rip Tide

Unsettling things are afoot in a sleepy Cornish village. Strangers are hanging about the harbour and a mysterious object is retrieved from the sea bed. Then the locals start getting sick.

Could this have anything to do with the alluringly beautiful Ruth who local lifeboatman Steve has taken a shine to... or could the other stranger, a man calling himself the Doctor, be somehow involved? And why is Ruth both drawn and terrified by the sea?

The Doctor is perhaps the only person who can help, but can he discover the truth in time?