Gathering the suspects together, Poirot reveals that the killer in all three murders is Jane Wilkinson. Her motive in killing Lord Edgware is that the Duke of Merton was an Anglo-Catholic and would not marry a divorced woman. She recruited Adams to impersonate her at the dinner party, while she killed her husband and then killed Adams afterward with a fatal dose of Veronal. The women met at a hotel to exchange clothing before and after the party. While waiting for Adams to return from the party, Wilkinson discovers a letter among Adams's belongings that had yet to be posted and tampered with to implicate the last man it mentions for the murders. Ross was killed because he realised that Wilkinson did not attend the dinner party; her ignorance of Greek mythology gave her away, as Adams had been knowledgeable on the subject and thus talked about it while impersonating her.