John Parker is a 43-year-old married man. His wife, Rachel, is a 40-year-old, voluptuous, attractive woman. John and Rachel have a comfortable marriage, although the sex has been lackluster for the last several years...a fact that does not make John happy.
John's older brother, Frank, is 47-years-old. John has looked up to Frank since the two were boys. Frank lives nearby in the same city, and they often get together and have remained close. Frank is married to Irene, his second wife, who is an attractive 37-year-old.
One night, very late, Frank instant messages John to tell him about a remarkable device that he has found. Frank works as an accountant in a research lab, specializing in some sort of top secret research. On the way to his car, Frank finds a strange looking device on the ground.
After fiddling with some of the buttons on the device, Frank discovers that it has some incredible capabilities, most notably the ability to cause the heads of two people to swap. Most incredibly, Frank realizes that the people affected accept the exchange as if reality had always been that way.
John, who is very skeptical of Frank's story, immediately asks Frank to come over. Since Rachel and Irene are not night owls, they are both asleep, and John and Frank often get together late at night.