British explorer Percy Foster (Charlie Hunnam) explores the mysterious Amazon jungle in South America and discovers signs of unknown civilization. He returns to Britain to make this profound discovery public, but is mocked as a joke and no one is willing to believe him. With the unconditional support of his beloved wife Nina (Sienna Miller), Foster is determined to lead his son Jack (Tom Holland) back to the Amazon jungle to search for evidence of the existence of ancient civilizations, but the group disappears strangely and has no news since then, becoming the most mysterious and suspenseful disappearance in history.