John Gillum arrives in London from Australia apparently a wealthy man and then proceeds to cheerfully gamble his entire fortune away. During this period he cultivates the friendship of Mortimer, the bank official after meeting him at the scene of a murder near the bank. He mentions in conversation that he felt suicide was a very understandable option to someone who had lost everything. When Gillum's body is found, the inquest duly returns a verdict of suicide and blackmail is suspected of being a contributory factor. However Gillum's cousin is so convinced that he would never have killed himself, he engages Thorndyke to try to find the blackmailers and bring all the issues to light...
