Four pals are stuck in a rut in adulthood: Adam has just been dumped, Lou is a hopeless party animal, Craig is a henpecked husband, and Jacob does nothing but play video games in his basement. But they get a chance to brighten their future by changing their past after a night of heavy drinking in a ski-resort hot tub results in their waking up in 1986.

A daring physicist travels into the past to stop a mysterious woman from stealing his invention. But once there, he uncovers a surprising truth about the machine, the woman, and his own fractured reality.

After their first adventure with the Hot Tub Time Machine, Lou and Nick are living very well off their ill-gotten gains, while Jacob still cannot rely on Lou to be a positive role model. When an unknown assailant breaks into Lou's mansion and shoots him, Nick and Jacob take him for another trip in the hot tub. They emerge in the year 2025, where they must figure out who shot Lou and prevent it from happening again.

Eric, the top investment manager at his firm, is assigned to help Julia, the stunning owner of a recently acquired company. He falls for her, and realizes he has to go back in time to meet her before she becomes engaged.