Four young friends, while taking a shortcut en route to a local boxing match, witness a brutal murder which leaves them running for their lives.

At the height of the Vietnam war, Captain Benjamin Willard is sent on a dangerous mission that, officially, "does not exist, nor will it ever exist." His goal is to locate - and eliminate - a mysterious Green Beret Colonel named Walter Kurtz, who has been leading his personal army on illegal guerrilla missions into enemy territory.

Unscrupulous boxing promoters, violent bookies, a Russian gangster, incompetent amateur robbers, and supposedly Jewish jewellers fight to track down a priceless stolen diamond.

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.

In Prohibition-era Chicago, musicians Joe and Jerry witness a mob hit, and flee the state in an all-female band disguised as Josephine and Daphne, but further complications set in.