Doctor Pemberton, an eminent Doctor with a practice in Harley Street, is murdered during a performance of Tchaikovsky music at the Albert Hall. Inspector Hadley and Sergeant Cooper are assigned the case but as they begin their investigation, Lady Beatrice Maitland, a patient of Doctor Pemberton, is found dead at the Savoy Hotel in mysterious circumstances. A post mortem reveals she had been murdered in a most ingenious way, which shocks her devoted husband, Sir Rupert Maitland, one of the wealthiest Merchant Bankers in the City. The detectives follow up every possible lead before Sir Phillip Doyle, a Director of a City Bank, is seen to leap into the path of an underground train at Farringdon station. Sir Phillip was a close friend of Sir Rupert Maitland, who now suspects that he will be the next to die at the hands of the killer. The investigation leads the detectives to suspect that Jonathan Hurst, a close friend of Lady Beatrice, may be the murderer, but he is found dead at the Colonial Club in Berkeley Square before they can question him. Sir Rupert leaves his London home for his country house in Northampton for safety at the moment that his brother is murdered in St. Pauls Cathedral. The detectives are overwhelmed by the number of unconnected murders which is made worse by the death of Sir Jocelyn Whittaker, a close friend of Sir Rupert, in a fire at his London home. Finally, the detectives trace and confront the murderer on a steam yacht moored on the Thames.