In the envelope was also a certificate of marriage between Ernestine Grant and Donovan Bailey. Mrs. Grant wanted to tell Patricia about her marriage to Donovan, because she knew that Donovan was in love with Pat. When she told Donovan about her intention he decided to kill her. A little trick with a bottle filled with an anesthetic helped Poirot to get proofs from Donovan’s pocket – the envelope and the key from Patricia’s flat.