By the summer of 1908, Sherlock Holmes has left the Baker Street days of crime and detection behind to take his retirement in a small Sussex cottage overlooking the sea. Holmes extends an invitation to his old colleague and confident, Dr Watson, to join him for a week's holiday. Accepting the summons, Watson arrives anticipating long coastal walks and pub lunches in the local village.

But his holiday takes a darker turn when they spot a shadowy figure below the cliffs one night; Holmes cannot resist the temptation to solve one more mystery and Watson realises he was never invited to the country for recreation. Against the backdrop of the stormy Sussex coast, suspicious men, tragic family history and a crafty theft weave an engaging and complex case that only Holmes and Watson can crack.