Professor John Waales, an anthropologist at U.C. Berkeley has spent his life in quest of a great find. He has been the assistant on many good projects, but every original project he tries winds up in failure. His wife died suddenly when he was on a failed mission out of contact with his family for six weeks. His daughter, who was 12 at the time never forgave him completely. He lost himself in his work and further alienated her. He has been working on finding the famed El Dorado, the legendary city made of gold hidden in the Andean Mountains near Bogota, the modern capitol of Columbia, for years. He is close friends with a chiropractor, Dr. Jack Paris, who takes care of him and his daughter. He has an assistant, Robin Quigley, who is secretly plotting against him to capture gold and the glory of the El Dorado treasure. He is also friends with the skipper of a W.W.II PT boat who takes him up the Amazon in search for the gold. His theory, laughed at by many of his colleagues, shows that the Chibcha Indians, who built the Lost City at Lake Guatavita, actually tore down the buildings covered with sheets of gold, took their treasures, and moved out of the mountains down several thousand feet to the Amazon jungle, along one of the many hidden tributaries. Here they hid from the outside world and were never heard from again, except by occasional sightings, all unconfirmed. This data had been gathered by Professor Waales and was now waiting physical confirmation.

There is an Ex-CIA spy, Thomas Reichen, who was kicked out of the Agency and was supposed to be terminated. They were unable to kill him and he changed his looks and his identity. He became a professional guide in Peru and Columbia and learned those countries inside and out. He has connections with the natives, terrorists, drug runners and gun dealers. He is hired by a Financier, Leon Scarborough, who is financing the efforts of the Anthropologist, but is actually working for a terrorist. The guide is told that once the City is found, then he will kill the anthropologist, his daughter, the chiropractor and the boat captain. This also works well for the Guide, because he will keep the Captain's boat and will return for supplies to set up a satellite relay / laser weapon which will serve the terrorist's country. They would keep the gold and also harvest, extract and sell cocaine from the Basin. Then the Assistant Anthropologist will take credit for the discovery of the site, the laser will be installed and the gold will be secretly removed. The assistant anthropologist will be told he will get most of the gold and the credit for the discovery, but he will be killed after the others once they discover the City. The plan is, that at the end, the Financier and the Guide will make it back to civilization with the help of the natives and will be thought to be dead along with the others.

What they also didn't count on was the presence of giant killer piranhas in the river around the new location of the famed El Dorado. These piranha were bred over 500 years ago with the local, non killer Pacu fish - a close relative which feeds on vegetation and also the giant pirarucu fish. The Pacu are much larger than the piranhas- some two to three feet in length, but have the same body shape as the piranhas and the pirarucu are one of the world's largest fresh water fish, as long as twelve feet in length and weigh several hundred pounds. When they were cross bred by the local kings who lived in the El Dorado, they eventually became giant killers, with Piranha teeth and a taste for flesh, but with the length of the much larger pirarucu and the girth of the fat pacu.