No one knew that Lord Charlton, one of Britain's wealthiest bachelors, had an heir until the terminally-ill textile magnate summoned his solicitor, Ambrose Quince, to his London townhouse in Belgrave Terrace. There he revealed that he wished to alter his will in favor of his nephew, the son of his black-sheep brother. The boy had been secretly adopted by American parents and taken to live in the United States when his own parents were killed in a bombing raid on London during World War II. His present whereabouts: unknown.

When Lord Charlton dies suddenly, he takes with him the secret of Simon Warwick's identity. Two men come forward claiming to be Warwick. Then one turns up dead in Ambrose Quince's office and Henry Tibbett, Chief Superintendent of Scotland Yard, is faced with a double mystery: Who is the murderer? And who is Simon Warwick?