Seventh Son by Linda McNabb

Jaxon is the seventh son of a seventh son.

He WAS an apprentice wizard - until he made a huge mess and was banished by his master, Wizard Argus.

A year later, travelling with Smokey, a troublemaking young dragon, he finds out someone is putting up wanted posters of him.

Who wants him and why?

Jaxon finds that someone is stealing magic and if they aren't stopped the world will begin to fall apart. Only the desert witch can help!