"Illusion" by Martina Boone is the final book in the "Heirs of Watson Island" trilogy. Barrie Watson is trying to break the curse that endangers her family without destroying the magic that protects Watson's Landing. She needs to mend the divisions between the island's families that have lasted for three centuries, solve the mystery of the Fire Carrier and the spirits he guards, and control dangerous forces. She finds an unexpected ally in Obadiah, but his help comes at a cost, leading Barrie into a perilous maze of magic, mystery, and intrigue.