In 1994, the Marines are testing a new missile, but after the launch it mysteriously disappears and it's clear that if the rocket reaches civilian areas they will be in big trouble. Carol Dawson, a journalist, is alerted by an unusual sight of whales in the Miami area, and decides to go and write about it.
Armed with special equipment provided by her friend, Dr. Dale Michaels from MOI (Miami Oceanographic Institute), goes to investigate the rumors of a missing missile belonging to the Marines and that could be behind the mysterious whale behavior lately. She hires the services of Nick Williams and Jefferson Troy, owners of a little boat so she can get to the Mexican Gulf and investigate closer if a missile has something to do with all of the above.
They end up finding an unknown artifact, bringing a lot of doubts about its nature, and even if it's part of a lost treasure that could be worth millions. Old friends of Williams and Troy noticed the finding and just like the old times, they want to steal it from them.
In the background of the story, the author talks about a submarine snake civilization on a planet called Canthor, and how they were struggling to stay alive due to new threats into their ecosystem. It's revealed later in the story that the artifact found in the sea is actually a cradle that contains seeds with altered superhumans, which were extracted from earth millions of years ago and were altered so they could live with other species (including the submarine snakes) on earth. The spaceship that carries the cradle is manned by robots/cyborgs and has hidden itself on Earth's ocean floor to make repairs.
Dawson, Williams and Troy found the damaged ship in the bottom of the sea while looking for the missile, and were asked to gather materials so the ship can be repaired and it could go back to its mission. Before leaving earth, the ship asked the humans to keep the cradle because it would enormously help the human race to have such superhuman seeds to develop faster and better through time, but in the end the humans refuse in order to avoid future wars between the human and superhumans.