In 2010 Los Angeles, three friends have had a string of bad luck with their adult lives: Adam (John Cusack) has been dumped by yet another girlfriend, and his video-game-obsessed nephew Jacob (Clark Duke) lives in his basement; Lou (Rob Corddry) is a party guy past his prime; and Nick (Craig Robinson) has a dead-end job and an unfaithful wife named Courtney (Kellee Stewart) who controls his every move.
Lou nearly kills himself in an accidental suicide attempt through carbon monoxide poisoning, although he denies that he was trying to kill himself. Adam and Nick impulsively take him and Jacob to the site of some of their most memorable weekends, the Kodiak Valley Ski Resort which, like them, has fallen upon hard times. After a crazy night of drinking in a hot tub, the guys wake up in 1986. The group can see each other as their proper age, but when they look at their reflections and to everyone else they appear as they did in 1986; however, Jacob, who has not even been born yet, is still in his normal 2010 state.
They arrive during "Winterfest '86," the weekend when Poison played to a huge crowd at the then-thriving Kodiak Resort. It is also a time that was particularly hard on the group: Adam broke up with his first girlfriend; Adam's sister, Kelly, conceived Jacob with an unknown father; Lou was beaten up by Blaine, the ski patrol bully; and Nick played a less than mediocre performance with his band at an open mike contest.
The quartet are at first concerned that if they change even the slightest thing in this time, it could have drastic consequences in the future, so they set out to do exactly what they did 20 years ago. Later however, they decide that this may be a chance to change their destinies and get the futures they always wanted; but when Jacob begins to flicker in and out, he warns the guys that if they continue what they're doing, then he may not ever be conceived.
Adam's girlfriend, Jennie (Lyndsy Fonseca), dumps him before he can dump her, but he ends up spending the night with a music journalist, April (Lizzy Caplan); Lou is beaten up by Blaine (Sebastian Stan), but this time finds the courage to fight back, with Adam and Nick giving him the motivation to stand up for himself; and Nick rocks the crowd with his band. Lou also seduces Kelly (Collette Wolfe) and conceives Jacob, thus solving the identity of Jacob's father.
Back at the resort, as the guys are set to go back to 2010, Lou decides to remain in 1986, admitting to Adam that he was trying to kill himself with the carbon monoxide poisoning, and that if he goes back it will happen all over again. He also says he wants to use his knowledge of future history to make investments, and do right by Kelly and Jacob.
Upon arriving back in 2010, Adam, Nick, and Jacob discover that Lou, Kelly, and Jacob are a happy family enjoying a lavish lifestyle, since Lou has shamelessly taken advantage of his knowledge of the future to become a successful rock star and Internet entrepreneur. Adam discovers that he eventually married April, and Nick is a successful music producer married to a loyal Courtney. The movie ends with Adam, Nick, Lou, and Jacob reuniting at Lou's mansion with their families, satisfied with their new lives.
