This is an addition to Dickson's fantasy series (The Dragon Knight, 1990, etc.) featuring a former college professor, Jim Eckert, and his wife, Angie, who have been transported to an alternate 14th-century England where magic works. Jim is apprentice to the powerful wizard Carolinus and he is also the Dragon Knight--since he can transform himself into a dragon. This time, Jim and Angie are requested to spend the 12 days of Christmas at the Earl of Somerset's castle. Unfortunately, problems--for which Carolinus expects Jim to provide solutions--rapidly pile up. Angie announces her intention to adopt an orphan baby, thus frustrating Jim's desire to return to the 20th century. The troll that has lived under the castle for 1,800 years complains that a rival troll has infiltrated the castle's human guests, while a troll army has mysteriously assembled beyond the castle walls. The local dragons demand to attend the Christmas celebrations. And Jim's magical competence is disputed by a wizard one grade higher than he. Agreeably 14th-century in ambience, whimsical in tone yet devoid of real humor, this overlong installment should please series fans, but won't tempt many newcomers.