The second book in the riveting new series that fans of Keeper of the Lost Cities and Percy Jackson can't put down. Twelve-year-old Alessia has just returned to start her second school year in the Lost City of Atlantis, when the underwater nation is gripped by some ominous news. A prisoner responsible for one of the worst attacks in Atlantis history has escaped, and Alessia suspects her fugitive, evil mother is involved. With the help of her schoolfriends, Alessia will have to interrogate some pretty reluctant merfolk, break into the underwater world's most secure prison, and master her newly-found mind-control power to find and stop her mother before the escaped convict finishes what he had started. But the more Alessia uses her power, the more she realises that this power comes with a sinister cost...