In an isolated house on the cliffs of north Cornwall the sibling rivalry between identical twins Max and Ashley Hennessy is coming to a murderous climax. As children they were always up to shenanigans - switching identities to create mischief. They both know one of them must die. But trapped in his wheelchair Ashley knows the odds are now against him he is in mortal danger - but does Detective Inspector Fergus believe him? And can he trust the mysterious Nurse Malahide who has been employed to protect him? Poor Lalla, the twins' eccentric old aunt is torn between the two boys: which of them is the victim and which the psychopath? As a force ten Atlantic gale threatens to plunge the old house into darkness news comes of a tragic accident on the cliffs and Lalla has to face the possibility that even she is unable to tell which of the twins is which. Perhaps they have done it once again - pulled off the final 'switch'.