An Orangutan is taken from his home in Malaysia after his mother is killed by hunters. A scientist buys him and names him Jupiter. He teaches Jupiter to use sign language to communicate, as well as putting some kind of chemicals in his brain to make him smarter. The professor is using Jupiter to hopefully one day cure "feeble-mindedness" in children. He is proud of Jupiter and shows him off to another man named Goujon. Goujon is fascinated by Jupiter and learns sign language from him enough to communicate. Goujon tells the professor that he believes Jupiter could be sold for a lot of money, but the professor refuses saying he wanted to continue his experiments on him and eventually do the same experiments on the "feeble-minded" children. One day, Jupiter is sitting in his room and Goujon returns and kills the professor to steal Jupiter and take him back to Paris to sell him. Jupiter doesn't understand that Goujon had killed the professor until he hears him telling the people he was going to sell him to about how the professor was mad and wanted to experiment on children, and how he didn't go without a fight. After Jupiter realizes what Goujon has done he refuses to cooperate, and does not demonstrate his signing abilities to the people he would have sold him to. Goujon tries to persuade Jupiter to cooperate by leaving him in a cell for a few days, but Jupiter still refuses. After a while for reasons that Jupiter doesn't understand, Goujon wants to steal gold from a woman in the city. He tells Jupiter that if he can help him steal the gold he can go back home. So Jupiter agrees, and climbs up the building the woman lives in and attempts to steal the gold. For some reason the gold is tied to the woman's wrist, so Goujon gives Jupiter a razor to cut it. But the woman's daughter comes home, sees Jupiter and screams, waking up the woman. Jupiter accidently slashes the woman's throat, and chokes the daughter to death out of fear. After he sees what happened, Goujon abandoned the scene, and Jupiter ran into a forest. A few days later, Jupiter finds Goujon again. Goujon explains that a detective has figured out that an animal had done the crime, and if anyone finds out that Jupiter could communicate and understand, they would both go to jail. So Jupiter goes to a zoo and pretends to be a normal Orangutan. The detective finds Jupiter in the zoo, and points him out for the murder. Jupiter wants to show him that he can talk, to make the detective look foolish somehow. But he doesn't, and stays in his cage.