The Curse of the Demon(1989)
(The fourth book in the Mostly Monsters series)
A novel by Mary Anderson
Cassie and Barney take a cruise to the Yucatan for fun and relaxation, but when a vengeful Mayan god comes to life and seeks revenge for his stolen jewels, the two young sleuths must solve the mystery.
Used availability for Mary Anderson's The Curse of the Demon
July 1989 : USA Paperback