The Lord Mayor has abused his trust: The city is poor, its buildings falling into decay while he squanders its wealth on pretentious follies. Some of the Emperor Charlemagne's advisors counsel violent revenge, but Isaac has a gentler remedy: He colors an ordinary mouse blue, perfumes it with precious spices, and trades it to the overweening--but foolishly gullible--mayor for all his treasure. Charlemagne arrives in time to witness the mayor's discomfiture when the ruse is unmasked, banishes him, and puts Isaac in his place. In a note, Manson attributes this amiable cautionary tale to ""a monk called Notker the Stammerer,"" who wrote it down in 884. His lavish illustrations boldly echo medieval illuminations, with elaborate initials and borders and decorative repetitions of figures framed in stylized architectural details; the large-eyed, rather squat characters have a touch of more up-to-date humor, still in harmony with the overall design. A bit busy, visually, but so is a Gothic cathedral. Good story, well set.