While playing with Tarzan Terk sees something that frightens her. She tells the others it was a scaly, green monster but the others are skeptical. Later, when Tarzan and the Prof. find a dead leopard they know Terk may be on to something. It appears that a Velociraptor from the underground world of Pellucidar has somehow made it to the surface and it's heading straight for the tree house.
—tomtrekp