A chance encounter as Holmes and Watson cross Westminster Bridge saves the life of a man preparing to leap into the Thames and certain death. It appears that he is a gambler who has been cheated at Bairstows, a gentleman's club in London. Thousands of pounds have been lost to a single 'lucky' member by betting on horse races at the club. Holmes must now discover how this trickery is being done and find a way to end his 'lucky' streak and avoid a scandal.