During the Mexican Civil War of 1913, Tom Bryan, a mercenary who wields a Lewis machine gun he dubs La Cucaracha, joins a band of revolutionaries led by Colonel Juan Castro. Though he’s paid for his services, Bryan is tired of the brutal, squalid life in Mexico and even starts to think about offering his talents to Cuba. Along the way, Ruth Harris, an American living in Mexico as a schoolteacher who becomes a soldadera after her father’s murder, travels with the group, bringing a quiet resolve to the dangerous journey.
Castro lays out a daring plan: a coordinated assault and robbery of a government train carrying a vast treasure of gold. The mission hinges on two freshly laid traps—Bryan’s disguise as a passenger, and the expertise of Pablo Morales, a dynamiter who will blow up a bridge to separate the two trains and clear the path to the gold. Castro senses treachery from Morales, recalling a robbery years earlier when Morales disappeared, but Morales’ wife vouches for him, insisting he is a loyal Villista and not a traitor.
After wiping out the Federales, the group seizes the government gold, with Castro intending to deliver the loot to Pancho Villa. However, Villa fails to show at the rendezvous, and Morales begins to win the loyalty of some of Castro’s men in an effort to keep the gold for themselves. Bryan, meanwhile, sees the gold as a means to fund his own revolution in another country, a lure that tempts him to seize the fortune for himself. He wastes no time, using his Lewis gun to cut down many of the opposition as he fights to keep the prize.
Morales, Ruth, and the others are ultimately captured by the Federales. Morales offers the gold, and even Bryan and Castro, in exchange for money and amnesty. Because of her American nationality, Ruth is escorted to Tampico to be deported back to the United States, while the others face execution. The pursuing government forces, aided by Yaqui trackers, close in, and the two leaders—Bryan and Castro—reconcile around the shared goal of survival and resistance, fashioning a gun emplacement from the bags of gold for a last stand.
As the Federales press the assault, Morales is sent forward with a white flag and a hand grenade, but Castro acts first and kills Morales. Castro is then killed by the approaching pursuers, and Bryan realizes the only way to prevent the gold from falling into enemy hands is to blow it up. The explosion triggers an avalanche that buries both the gold and the pursuing soldiers. Left unarmed and broke, the solitary Bryan makes his way toward Tampico to reunite with Ruth, carrying the weight of a hard-won, morally complex victory.
Looking back on the wreckage and the lives spent for the gold, Bryan tells the circling vultures that if they ever feasted on Castro, they would have feasted on a real man.
