Mrs. O'Malley and Mr. Malone (1950)

"Murder-on-the-train" mystery has lawyer Malone chasing his paroled embezzler client (Kepplar) who still hasn't paid Malone's fee. When Kepplar jumps parole on a train to Chicago, Malone follows, in company with Kepplar's ex-wife, a police inspector and Mrs. O'Malley, a hearty radio contest winner from Montana. Kepplar is murdered, and a game of musical corpses commences, with hijinks in coach corridors as Malone and Hattie search for the killer.