In London's famous Burlington Arcade a man grabs a handful of jewels and flees. A bored Poirot is meanwhile musing on becoming a master criminal himself. At her request, he meets Lady Millicent Castle Vaugh who explains that she is soon to marry the Duke of Southshire but is being blackmailed by an ex-lover. Poirot now has the excuse he needs to realize his criminal ambitions and proceeds to break into the suspected blackmailer's flat.