Zack Mayo is a young man who has signed up for Navy Aviation Officer Candidate School. He is a Navy brat who has a bad attitude problem. GySgt Foley is there to train and evaluate him and will clearly find Zack wanting. Zack meets Paula, a girl who has little beyond family and must decide what it is he wants to do with his life.

Bent on unearthing the cynical traitor who sold information to the enemy and caused the death of a dear brother-in-arms, the battle-tested former Union cavalry officer, Colonel Cord McNally, teams up with a pair of ex-Confederates after the Civil War. Now, as honest friends, the three companions ride into Rio Lobo--a dusty town in the middle of the desert overcome by corruption--to bring to justice the one who sold McNally out; however, the town is rife with the betrayer's murderous cut-throats....