Marshal Chris Adams turns down a friend's request to help stop the depredations of a gang of Mexican bandits. When his wife is killed by bank robbers and his friend is killed capturing the last thief, Chris feels obligated to take up his friend's cause and recruits a writer and five prisoners to destroy the desperadoes.The last in the original series of four "Magnificent Seven" movies.

In this third remake of legendary Japanese director Akira Kurosawa's hugely influential The Seven Samurai, the seven gunslingers (George Kennedy, Michael Ansara, Joe Don Baker, Bernie Casey, Monte Markham, Fernando Rey and Reni Santoni) liberate Mexican political prisoners, train them as fighters and assist them in a desperate attack on a Mexican fortress in an attempt to free a revolutionary leader.