Three scientists came to the mysterious planet Nacre to discover, to explore, to record. Utterly defenseless, they trekked through the grotesque jungle of multiform mushrooms and dense spore-clouds, hoping to unlock the secret of this strange world. The stunning climax of their mission was just the beginning of a complex drama in which their survival—and return to earth-could spell the extinction of humanity.

The trio of scientists had been ordered to survey the planet's flora, fauna and mineral resources, and from the very beginning of their mission everything they observed led to one startling conclusion-the mysterious world was virtually identical with the Earth of the Paleocene period, 70,000,000 years ago at the very dawn of the age of mammals! Their names were Cal, Veg, and Aquilon, the most resourceful-and rebellious-of Earth's explorers, and with them came four alien companions, the mantas. Strange flying beings, half-animal, half-fungus, the mantas possessed the keenest senses of any creatures in the universe, a gift which immediately saved the mission from complete disaster. Detecting strong vibrations coming from a great distance, the mantas warned the humans, and Cal realized that it could mean only one thing: an earthquake-one large enough to produce a tidal wave that would totally inundate the small island where they had set up camp. Veg, the strongest member of the team, constructed a crude sailing raft, and the party put out to sea to escape the doomed island. It was the beginning of an incredible series of adventures which would lead them to discoveries as momentous as they were deadly. Sailing for weeks, the raft took them to a region vastly different from the island they had left behind. And when a brachiosaurus, supposedly extinct in the Paleocene period, nearly swamped the raft, they knew they had reached an area of priceless scientific value-an isolated enclave of the Cretaceous period where the full spectrum of the golden age of reptiles was present! But just as incredible as the dinosaurs was another creature they were soon to meet-Orn, a man-sized bird who belonged to the most advanced species ever to develop on this world. Unsurpassed racial memory enabled Orn's mind to reach millions of years into the past, and it was his presence that led the three humans and the mantas to open revolt. Determined to prevent man's destructive exploitation of this world, they must pit themselves not only against the creatures they wish to save from extinction, but also against the all-consuming greed of Earth's powerful authorities. As rich in scientific detail as it is in breathtaking excitement, Orn is a masterwork of the imagination and a tribute to the creative genius of Piers Anthony.

Cal, Veg, and Aquilon try to escape from a dangerous world ruled by murderous robots and return to their own dimension