In London, Ellie and Alvin have been married nine years and are bored. Things could be worse, though. Their friends Peter and Janet have two kids and their sex life is nearly non-existent. His sex life is another matter, but that's another issue. Co-workers of both Ellie and Alvin make suggestions about what to do to spice up the marriage. Ellie seems to be a fashion designer, and Alvin works with blueprints. One idea is swapping with another couple, which leads to some laughs. Ellie puts an ad on a web site. We meet some of the more colorful couples who are being considered. One couple is selected, and things go pretty well at first. Once a couple is selected, the process all seems perfectly innocent and not dirty at all. But ultimately the plan is not successful, and the rest of the movie is about whether Ellie and Alvin will even stay together, as well as the breakup of Peter and Janet's marriage over his cheating. By the end of the movie, there is hope for at least one, and possibly both, of the couples.