Accompanied by Holmes and Watson, Mrs. Hudson crosses the ocean to attend the wedding of her cousin's daughter. They disembark to discover that the young lady's fiance, a pitcher for the Brooklyn Bridegrooms, stands accused of an attempt on the life of JP Morgan and the death of his aide. A self-declared enemy of Morgan and the robber barons, the ballplayer ran from the scene of the crime and, when captured, was found in possession of a gun with two spent cartridges, the same number and caliber as that used in the attack. Before a wedding can be held, the unacknowledged sage of Baker Street will lead Holmes and Watson along a path of investigation taking them from JP Morgan's mansion to the gambling dens of New York's Tenderloin."