Wizard Kadmeion and his assistant Sir Bright promised Lady Luck's daughter, Probability, a getaway to see unicorns. Bright's brother tends a herd of the captivating creatures on Wuddlekins Island. During their visit, Kadmeion plans some quiet time studying the local boggart magic. But their visit soon becomes troubled. Something is sickening the unicorns' magic, and the illness is spreading to neighboring islands. Without unicorns, the magic in Kadmeion's plate-shaped ocean world will fall into disarray. Just when things could not get worse, Bright's parents drop by Wuddlekins for a visit. The unicorn problem is nothing compared to what Bright's aristocratic father has planned for his twice-seventh son. Kadmeion and Bright must somehow fix the unicorns' magic, see to an elf-prince's demands, and make sure that Probability has a wonderful vacation. After all, it is unwise to disappoint the future Lady Luck.