August 1976 and it seems as though the long hot summer will never end. Early morning at Clacton on the north Essex coast, a light aircraft takes off from the airstrip but struggles for height and crashes into the sea. First on the scene, Sgt Cyril Claydon pulls the pilot's body from the wreckage. But something else catches his eye. A bulky package wrapped in black plastic is on the passenger seat. Returning to investigate, he makes a grim discovery...