On “Emerald Island,” a female inmate at a women’s prison is buried up to her neck in quicksand, and is strangled to death by a boa constrictor, as other prisoners hear her screams. Elsewhere, in an unnamed city, Miss Daly enters a high-rise building, shoots the security guard in the head, and takes the elevator to see Mr. Luker, a gem dealer. She holds him at gunpoint, and tells him she was an enslaved prisoner on Emerald Island for two years, forced to spend her days digging in the mud for gemstones in South America, all to benefit Luker’s business. Luker feigns ignorance, telling Daly that he used middlemen to procure his precious stones. However, she does not believe he had no knowledge of the tyranny. Enacting her revenge, Daly tells Luker of the events that led her to him. She sent a “plant” named Maria into the prison, posing as a new inmate, and her partner, Laredo, and his band of jewel thieves, to steal Luker’s emeralds. Maria was transported to the camp by prison guards on a riverboat under the command of a local named Captain Orinoco. Elsewhere, Laredo and his men planned to attack the guards and force Orinoco to lead them to the prison. However, Laredo is ambushed by armed guards, and most of his men killed. Meanwhile, Orinoco leads the guards and inmates to his camp to rest for the night. During the night, Maria seduces the head guard, and he is stabbed in the back by Laredo. Laredo offers to pay Orinoco to take them to the prison. Elsewhere, the inmates are forced to dig in the mud for emeralds, and the warden, Cesare, is disappointed by their poor results. The hostile prisoners fight each other at the slightest provocation. A woman named Muriel is tied to a post and left to bake in the sun after being caught fighting another inmate. Maria sneaks off to bathe, and is raped and beaten by two guards. Laredo arrives at the camp, posing as a new guard, and is shocked by the ill treatment of the women. He cuts Muriel down from the post and treats her wounds. Sometime later, the guards taunt Muriel by holding a snake to her face, and she bites the reptile’s head off. Maria admires her courage, and reveals to Muriel that she was sent there with Laredo and his jewel thieves to steal the emeralds. Muriel agrees to organize the women to fight with Laredo. In time, the inmates beat and drown an abusive female guard, who was a previous inmate, and the guards whip the women to make them reveal the killer. One of Laredo’s men leaps to the women’s defense, and Laredo punches him for fear that he will reveal their identity. When Paco is locked in a cell, Laredo readies his men to stage their revolt. Under the cover of darkness, they attack the guards one at a time, and set off explosions that rouse the prison camp. The inmates assist in the fight, and Maria blows up a safe with dynamite, taking two bags of emeralds. However, Orinoco steals the stones, but Laredo allows him to leave with one, keeping the other bag for himself. Laredo leads the women through the jungle where they encounter leeches, snakes, and quicksand, as the guards pursue. After Laredo is fatally wounded by a bullet, Maria and Miriam, the only surviving inmates, refuse to let him die alone. They take his unconscious body with them on a raft, and flee the island. Daly finishes telling Luker the details of the heist and escape, and asserts that the emeralds were lost in quick sand. After killing his henchman, she orders Luker to open his safe. Luker removes a gun from inside, but Daly shoots first, killing the gem dealer. Afterward, she stares blankly at a large diamond hidden in the safe.