Marty and Doc are at it again as the time-traveling duo head to 2015 to nip some McFly family woes in the bud. But things go awry thanks to bully Biff Tannen and a pesky sports almanac. In a last-ditch attempt to set things straight, Marty finds himself bound for 1955 and face to face with his teenage parents -- again.

Prot is a patient at a mental hospital who claims to be from a far away planet. His psychiatrist tries to help him, only to begin to doubt his own explanations.

When a huge alien probe enters the galaxy and begins to vaporize Earth's oceans, Kirk and his crew must travel back in time in order to bring back whales and save the planet.

A police chief in the war-torn streets of Los Angeles discovers that an extraterrestrial creature is hunting down residents - and that he is the next target.

The final installment finds Marty digging the trusty DeLorean out of a mineshaft and looking for Doc in the Wild West of 1885. But when their time machine breaks down, the travelers are stranded in a land of spurs. More problems arise when Doc falls for pretty schoolteacher Clara Clayton, and Marty tangles with Buford Tannen.