In the story, Sir James Damery engages Sherlock Holmes' services on behalf of an anonymous client. The honorable client is concerned for Miss Violet de Merville, the beautiful daughter of an old friend, who has fallen in love with a charming but extremely dangerous man named Baron Gruner. Since Miss de Merville will not hear a word against Gruner, Holmes must uncover irrefutable evidence against the Baron in order to dissuade the lady from marrying him. It is not an easy task, for Gruner is both cunning and ruthless - and those who opposed him in the past (as the Baron reminds Holmes) have all "coincidentally" come to harm.