After the corpse of George Hawken had been found on the rocks near his Cornish home the coroner's jury brought in an open verdict. Hawken had been a respected but financially unsuccessful artist whose death benefited no one except one of his nephews, who inherited a modest cottage. Yet that nephew had mysteriously disappeared. There was no doubt about the death of Hawken's brother, Sir Matthew, which followed not long afterwards: five grains of potassium cyanide had killed him instantly. Inspector Arnold and his friend Desmond Merrion were faced with a paradox: those who had had an opportunity to commit both crimes had no motive; no one with a motive had had the opportunity.