The Merlin effect is a kind of immortality bestowed by Serilliant, a shell-shaped horn fashioned by the craftsman Emrys as a gift for his mermaid bride, Wintonwy. Merwas, king of the met-people and Wintonwy's father, placed a rainbow colored liquid into Serilliant that would hold the power of eternal life -- for those who understood it. Serilliant came into the wizard Merlin's hands and, because of his arrogance (he even renamed Serilliant ""the Horn of Merlin""), Merlin lost it. But all that was over a thousand years ago. Presently, Kate Gordon, 13, is spending the summer with her father, who is doing research in Baja California. Jim Gordon is a historian specializing in Merlin, and he has reason to believe that the Horn of Merlin is buried with a sunken ship, the Resurreccion, just off the coast. The problem is that he can't prove it because an enormous whirlpool makes getting close impossible. Well, not quite impossible: Kate is sucked into the whirlpool during a storm and finds the Resurreccion, Serilliant, and even Merlin himself. She participates in a sorcery-filled adventure, saves Serilliant, and proves her worth by returning it to its rightful place. No matter how you slice them, Arthurian legends are magical. T.A. Barton (The Ancient One, 1992, etc.) may not be in T.H. White's league, but he'll do.