A strange prehistoric beast lurks in the depths of the Amazonian jungle. A group of scientists try to capture the animal and bring it back to civilization for study.

Lucas: I can tell you something about this place. The boys around here call it "The Black Lagoon"; a paradise. Only they say nobody has ever come back to prove it.
Lucas: It is impossible. But I, Lucas, will do it.
David Reed: We didn't come here to fight monsters, we're not equipped for it.
Kay Lawrence: And I thought the Mississippi was something.
Lucas: What kind of fishing is that? Who eats rocks?
Carl Maia: I eat rocks, in a manner of speaking. I crush and look inside them and they tell me things.
Lucas: What do they tell you?
Carl Maia: How old they are.
Lucas: There are many strange legends in the Amazon. Even I, Lucas, have heard the legend of a man-fish.
Kay Lawrence: Hurry, David.
David Reed: I've almost got it.