The BMW parked by the lake belongs to Patrick Gillard and the murdered man looks uncannily like Patrick, but Detective Chief Inspector James Carrick cannot bring himself to believe that his friend is dead. When Gillard's mother identifies her other son, Lawrence, Carrick realises it's a clear case of mistaken identity, for Patrick was a government agent and Lawrence a slightly down-at-heel and disorganised teacher, loved by everyone who knew him. A quick probe into Lawrence's life is called for, just for form's sake, but what Carrick discovers takes him by surprise and leads him into more danger than he has ever encountered...