Moonsinger by Andre Norton
It was the time of the Moon of the Three Rings, when the Free Trader ship Lydis landed on the planet Yiktor. The life of a Free Trader was all junior crewman Krip Vorlund knew, until he was strangely attracted to a delicate and mysterious woman named Maelen, caught up in a power play by outsiders seeking to control the planet, and found his mind trapped in the body of a wolf like creature. Krip would again inhabit a human body, though not his own, and on a second planet, Thoth, he and the crew of the Lydis would be caught in a battle of ancient powers and nameless evil. Only Maelen the Moonsinger could save them with her superhuman powers, if she didn't bring death and destruction instead.