Ox — Piers Anthony

Cal, Veg, and Aquilon -- two men and one woman -- roamed the alternate dimensions of time and space. With them were the mantas, strange flying aliens--half-animal, half-fungus -- who could boast the keenest senses of any creatures in the universe. And with them too was the mysterious, impassive super-woman, Tamme.

Now they were imprisoned on a hostile world dominated by savage robot machines. It was crucial to their very survival that each find a way back to their familiar dimension of Earth.

Suddenly they encountered the pattern named OX -- an amorphous, telepathic being of brilliant luminosity -- who held the key to every alternate dimension in the universe, including their only chance of escape!