Rider of the White Unicorn (Book 4‪)‬

… He looked down—straight into a pair of fiery yellow-green eyes. … Mark caught a glimpse of a cavernous mouth full of sharp yellow teeth. The creature seemed to have no substance, but changed shape more rapidly than clouds in a high, blustery wind. Its eyes winked on and off. … Each time they reappeared they came closer. … Then suddenly the air seemed to get even colder and he saw there were two pairs of baleful eyes. … Sharp icicles seemed to ripple through his bloodstream as realisation dawned: the creatures slowly circling him were trying to freeze him to death.

The search for the golden key of the Tower of Kaleidoscopic Light has brought Mark and Esmé, separately, down into a terrible place of darkness and death where terror stalks them on every side. And it seems that even in Castle Lazarone treachery lurks …