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 is an old friend – with a new face. The Doctor and his companions arrive on a pleasure beach in the 1970s, hoping for some time off. 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 there is a sinister prescense lurking in the cold sea – and it’s got designs on humanity. An adventure of the Fifth Doctor, taking place between Warriors Of The Deep and The Awakening.