Midnight at the Well of Souls — Jack L. Chalker

PLANET OF GODLIKE POWER

Below-average in height and unprepossessing in appearance, Nathan Brazil was an unassuming if cynical starship owner, carrying passengers and cargo for hire. Hardly the sort of person to hold the fate of the entire universe in his hands.

But when he detoured from his route to answer a distress call, a hidden stargate hurled him and his passengers to the Well World, the master control planet for the cosmos. Billions of years ago, a godlike race had unlocked all the secrets of space and time and remade the universe according to their grand design. Then they vanished and left behind the Well World to maintain the pattern of the universe.

Now someone was searching for the planet's hidden control room--the Well of Souls--to seize control of all the cosmos. Nathan had to stop them. But this planet wrought bizarre metamorphoses on visitors, changing them into alien forms--centaurs, mermaids, giant insects-- seemingly at random. Nathan could no longer, recognize his friends, let alone his unknown enemies. His task seemed hopeless, until his long-suppressed memories began to return, and he realized who he really was.. .