The two explorers Vallier and Gregson are traveling through an as yet unexplored area of a rain forest looking for unknown species of butterflies. They are accompanied by their interpreter Cook and a group of porters. Vallier is suffering from a jungle fever but tries to hide this fact from the rest of the group. Gregson is fascinated by the colorful butterflies. Cook tries to convince the others to return to the town they started from. As they reach a strange dark tunnel formed by climbing plants Cook manages to persuade the porters to turn back. Vallier and Gregson are left alone without any provisions and without the cage with the butterflies they have already collected. Despite the complications they decide to go on towards, because Vallier is obsessed with the idea of the unique black butterfly. In 100 years, only one copy is born and it is said to have very special skills. Driven by this fact, they exceed the TERRA LIMES