'Mr Gabb, your son did not commit suicide.  He was murdered.'

Simon Gabb has everything - or so it seems: a beautiful house, a big estate, a flourishing business and two sons, both endowed with evident capacity for carrying on the family firm.  The moody Giles is brilliant and inventive; the married Basil is dependable and efficient.  And yet something is manifestly wrong.  A secret invention, on which his business was engaged for the government, becomes known to those who had no right to know it.  But how and where did the leak occur? It is a conundrum which creates suspicion and dissension within the family and engulfs everyone who dine with them one Saturday night.  Giles has become friendly with young Arden and Billy Laforte, who were the previous owners of Herons' Hall until their father's death left them penniless, and who now rent one of the lodges on the property.  When Giles brings the Lafortes to the Hall for the first visit to their old home in three years, the Gabbs hardly know what to expect.  Yet the Lafortes seem completely at ease, so when a fierce storm develops, Mrs Gabb insistes they stay the night. 

The next morning, Gabb's elder son, Giles, is found dead in a motorboat on the lake, his body propped up by a shotgun. But it is soon apparent that the gun was not the cause of death, nor did he die in the boat; a skilled marksman shot him from a distance.  Superintendent Mallett is assigned the case and must deal with the smouldering emotions the flare up between everyone present that evening.