Kyle Perry, a married accountant who has a wife and two children, observes a fellow male commuter on the train one day as the man picks up a call girl. Kyle gets off at the same stop as the hooker and her current client. After seeing how affectionately the two behave with each other, Kyle decides to follow them down an alley near his destination. Having picked a cozy spot, the pair enjoys what looks to Kyle like some serious passion: not what he’d expect from a john and a hooker. Overcoming his shame, he watches their bout of lovemaking, but feels guilty afterwards for having indulged in voyeurism. His lapse into questionable behavior produces some unexpected results when he goes home, where, driven by erotic images of the licentious lovers, Kyle enjoys comparable passion with his wife.
Over the next few weeks, Kyle sees the same guy pick up two other women: a college coed and a housewife. Having again followed the lovers, he sees with surprise the same extreme level of passion exhibited by both the Commuter Casanova and his new partners. Once again, Kyle enjoys a gratifyingly high level of passion with his wife, Mandy, who realizes that something has produced a welcome change in her husband. When Kyle finally admits to peeping on the Casanova, Mandy reacts in an unexpected manner. She grows just as sexually excited by the stories of his voyeurism as he did by actually peeping on the lovers.
When Kyle sees the same guy reject the advances of a hooker on the train, he yields to intense curiosity, and confronts the man, who reveals an intriguing secret about his two-timing ways. Shocked but fascinated, Kyle finds that his life now changes drastically as a result of this revelation on the part of the Commuter Casanova.