They couldn't have celebrated happier anniversaries if they were married to each other.
A man and woman meet by chance at a romantic inn over dinner. Although both are married to others, they find themselves in the same bed the next morning questioning how this could have happened. They agree to meet on the same weekend each year. Originally a stage play, the two are seen changing, years apart, always in the same room in different scenes. Each of them always appears on schedule, but as time goes on each has some personal crisis that the other helps them through, often without both of them understanding what is going on.