Hard-working but mundane, near-future alien-visitor yam, as journalists, treasure-hunters, the US Navy, and alien super-robots mix it up beneath the sea off the Florida Keys. Ostensibly to investigate some unexplained whale beachings, but actually following the disappearance of an experimental Navy missile, journalist Carol Dawson charters the boat of disgruntled treasure-hunter Nick Williams and his jovial black sidekick, Troy Jefferson. Diving to the sea bottom, Carol and Nick discover--not the missile, but a peculiar golden trident. To complicate matters, repressed Navy commander Vernon Winters soon shows up, as does repulsive boat captain Homer Ashford--he once robbed Nick of a salvaged treasure. However, on a subsequent dive, Carol and Troy plunge into an underwater chamber, actually a spaceship full of weird shape-shifting robots. Seems that the damaged alien ship needs, in order to make repairs, information--plus large quantities of lead and gold. So, with some alien super-help, Carol, Nick, and Troy will hold off the Navy, relieve Ashford of the gold he stole from Nick--oh, yes, and save the entire human race. The gold trident, you see, contains genetically enhanced embryos--superhumans, too--for the aliens to release on Earth; instead, out of gratitude, the aliens agree to take the trident away and allow humanity to develop at its own pace. Lots of healthy character-building, such that everyone ends up with what they really need (Carol her story, Winters his God, Nick his significant relationship, Ashford his comeuppance), and some absorbing alien goings-on--but not too much besides. Clarke's ideas often take wing, but here he's just muddling through.