Paleontologist Joshua Green has no idea what he's getting into when his friend Lon Sanger shows him an ancient hu man skull coated in black ceramic, with gemstones for teeth and a huge emerald in one eye socket. When carbon dating suggests that it is older than mankind, Joshua prevails on Lon's smuggling connections to outfit an expedition to the remote Colombian jungle where it was found. Captured by cannibals, the survivors escape into a maze of tunnels and an underground city. There Joshua learns of the cycles of time that may now be coming to a premature end un less he can negotiate with the phantoms of the past. Unfortunately, the familiar if colorful jungle opening section all too soon gives way to a sometimes clever but undramatic time-travel yarn that of ten sounds like so much double talk.