Strangers on a Train (1951) plot summary
While on a train, famous tennis player Guy Haines is recognized by a fan called Bruno Anthony. During their discussion, Bruno comes up with the idea that since they both want someone in the lives to be killed or have them go away, that they should commit the other guy's murder so that neither of them will be suspect to the crimes, meaning that if Bruno kills Guy's wife, then Guy will return the favor and kill Bruno's father. But Guy takes this as a joke at first until he finds out that his wife has been killed by Bruno. Now that Bruno is stalking Guy, insisting that Guy return the favor, Guy must now decide whether or not to kill Bruno's father.
Submitted by Big Evil