wˌaɪl ˌɔn ɐ tɹˈeɪn tə sˈiː hɪz wˈaɪf, hiː mˈiːts tʃˈɑːɹlz ˈænθəni bɹˈuːnoʊ, ɐ sˌaɪkoʊpˈæθɪk plˈeɪbɔɪ hˌuː pɹəpˈoʊzᵻz ɐn aɪdˈiə tuː "ɛkstʃˈeɪndʒ mˈɜːdɚz": bɹˈuːnoʊ wɪl kˈɪl mˈɪɹiəm ɪf ɡˈaɪ kˈɪlz bɹˈuːnoʊz fˈɑːðɚ; nˈiːðɚɹ ʌv ðˌɛm wɪl hæv ɐ mˈoʊɾɪv, ænd ðə pəlˈiːs wɪl hæv nˈoʊ ɹˈiːzən tə səspˈɛkt ˈiːðɚɹ ʌv ðˌɛm.
While on a train to see his wife, he meets Charles Anthony Bruno, a psychopathic playboy who proposes an idea to "exchange murders": Bruno will kill Miriam if Guy kills Bruno's father; neither of them will have a motive, and the police will have no reason to suspect either of them.