A Wizard in Mind — Christopher Stasheff

Something is rotten on the Planet of Petrarch. It will take a wizard to set things right. Fortunately, one is available.

Magnus D'Armand, the renegade son of Rod Gallowglass, Warlock of Gramarye, has set out to prove himself twice the hero and liberator his father ever was. However, Magnus has inherited not only his father's awesome psychic gifts, but his uncanny knack for getting into trouble as well.

A WIZARD IN MIND
The First Chronicle of Magnus D'Armand
Bored and in search of excitement, Magnus D'Armand has asked his sentient starship to find him a world in need of revolution. But on the lost colony world of Petrarch, he finds far more than he's bargained for. Not only have a brace of warring princes plunged the planet into a dark age of bloodshed and betrayal, but a mysterious rival from Magnus's past is plotting his destruction. Even the Rogue Wizard will need a miracle to get himself out of this one!