Based on the historical novel by Walter Noble Burns, after his wife and brother are murdered, a Mexican farmer gets revenge and leads bandits against Anglos.
In California in 1848 Joaquin Murietta (Warner Baxter) and Rosita (Margo) are going to marry. Tomas (George Regas) says Americans take property from Mexicans and throws a knife at Captain Osborne. Joaquin says he threw it, and Rosita's father tells him to leave the ranch. Joaquin and Rosita wed. News of gold spreads, while Joaquin farms potatoes. Joaquin tries to stop Tomas from ambushing the wagon of Bill Warren (Bruce Cabot) and Johnny Warren (Eric Linden). Tomas is killed, and Bill's wound is treated at Joaquin's home. Rosita tells Joaquin that two Americans are digging on their land. Bill and Johnnie consult Judge Perkins. Four Americans tell Joaquin to leave or be killed. They beat him up, and he finds Rosita on the bed dying. Joaquin goes after each of the four men, roping and dragging one and killing another in a fast-draw match. Rewards are posted for him and the bandit Three-Fingered Jack (J. Carroll Naish), who wonders why Joaquin left the miner's gold.
The sheriff sends a posse after Joaquin, who walks in and complains he is being treated as a bandit. Bill tells Joaquin that killing is against the law and warns him to leave, promising to care for his madre (Soledad Jimenez). Joaquin works on the farm of his brother Jose Murietta (Carlos De Valdez). Americans in town bully Mexicans, and Pete (Harry Woods) claims Jose's mule and hits him. Jose is lynched, and Joaquin is whipped. At Jack's bandit camp Joaquin says he is the leader, and he wants more men. They steal horses and rifles and then pillage settlements. Joaquin's camp has women. Pedro tells Joaquin of a meeting of Mexicans. Ramon de la Cuesta speaks against fighting. Joaquin and his men come in and take the valuables. Juanita (Ann Loring) reprimands Joaquin, who leaves without the loot. Joaquin visits his madre. He finds Juanita, who joins him.
Bill refuses to join a posse against Joaquin. Juanita urges Joaquin to go to Mexico. Pedro tells Joaquin of a stagecoach carrying gold. Joaquin and his men rob the stagecoach; but Louise (Kay Hughes) faints from a wound. Joaquin drives her in the stagecoach to town, and Johnnie says his fiancée Louise is dead. Jack leaves a hostage, who fell into the river. Bill says that Joaquin and his men must be wiped out. A large posse rides and finds the hostage, who tells them where the hideout is. At their celebration Joaquin says revenge is no good and that he's going to Mexico. The posse attacks, and many are killed in the gun battle, including Juanita and Jack. Joaquin escapes on a horse, is shot by Bill but gets away. Joaquin takes flowers to Rosita's grave and dies.
This drama portrays the increasing violence caused by racial prejudice and unjust behavior of a minority. In this case fortune hunters from the United States took territory and then property from Mexicans. The story mirrors the racial violence and lynching in the United States as well as contemporary atrocities in Nazi Germany and the Japanese empire.