When a lighthouse keeper reports seeing a ball of light plunging into the sea off Tayborough Sands, UNIT sends Mike Yates to investigate. The last thing he expects to find there is an old friend — with a new face...

The Doctor and his companions arrive on a pleasure beach in the 1970s, hoping for time off after their latest adventures. But they do not get to relax for long. Violent incidents are at an all time high in the area and people are going missing — or else changing into something more than human...

The Doctor soon realises a sinister presence lurks in the cold seas off Tayborough Sands — a presence with sinister designs on humanity.