Myth Directions by Robert Asprin
When a girl (lushly curved, with a mane if light green hair) asks for a favour, a chap would have to possess a heart of stone (or a testosterone deficiency) to refuse. Court magician to the kingdom of Possiltum, Skeeve is a chap all right - and heads off with Tanda into the dimensions. The quest: to steal The Trophy on which Tanda has set her heart. Naturally, he bogs it.