 Tennis star Guy Haines meets a stranger on the Washington-to-New York train who offers to exchange murders. The stranger, Bruno Anthony, will kill Guy s estranged wife if Guy will kill Bruno s hated father. Guy doesn t take Bruno seriously until his wife, Miriam, is found murdered in an amusement park. Guy becomes the chief suspect, which threatens his tennis career, his romantic involvement with a U.S. senator s daughter, Anne Morton, his hopes for a political career, and even his life. When it becomes evident to Bruno that Guy isn t going to kill his father, he tells Guy he intends to establish Guy s guilt conclusively by planting his monogrammed cigarette lighter on the island where Miriam was murdered. With Anne s help, Guy attempts to stop Bruno after rushing through an important tennis match and racing to the amusement park.