Its Roger's birthday and Jeannie and Tony throw a small party for him. Instead of a normal gift Jeannie decides to give Roger something he has always wanted, his very own wish. As Roger is leaving the house, Tony mentions the fact that the next day he is going on an important space flight and Roger then blurts out that he wishes that he was going on that flight and at that instant, Roger and Tony switch bodies. When Tony realizes what has happened, he and Jeannie go searching for Roger not only before he goes on the mission, but to keep Dr. Bellows from finding out what happened. (thetvdb.com)