In a London secret society headed by lawyer Thaddeus Merrydew, pacts are signed among the members bequeathing their assets evenly to the remaining members. Members start dying quickly, and a widow asks Sherlock Holmes to look into her husband's mysterious death, leaving her penniless. Holmes zeroes in on a Chinese widow, Mrs. Pyke, and Merrydew as the possible masterminds. But Holmes' foes are crafty and stay one step ahead of the detective with more murders and little evidence to prove their guilt. Holmes must use his famous skills before a young unwilling society inductee is murdered.