ESCAPE FROM ATLANTIS

A disastrous family sail into the Bermuda Triangle strands two cousins on an uncharted island with unusual—and sometimes dangerous—residents.

Stocked with characters and creatures that will attract younger members of the Percy Jackson fandom, this opening escapade begins with an attack by a sea monster that casts 13-year-old Riley and her alienated, pestiferous 12-year-old cousin, Alfie, ashore on Atlantis, an island where time has slowed down. There, mutually hostile camps of magical creatures and stranded humans, who are gradually turning into talking beasts of various sorts through a process called “de-evolution,” steer suspiciously clear of each other. Eager to escape—and driven by the possibility that his mom and her dad might also have survived the attack—the cousins put aside their antipathy to enlist local allies and, by the end, to engineer, as titularly promised, an escape. O’Hearn further cranks up the mythological vibe by chucking in a siren (friendly), feral mermaids and unicorns (not so much), lotuslike Memory Berries that rob the eater of both recall and the desire to leave, and giant gargoyles that turn to stone in sunlight. Riley is outraged to discover that the partially transformed people—including a mild-mannered koala who positively channels Mr. Tumnus—are exploited as labor but ostracized for their physical differences by the nonaltered. Main human characters follow a White default.

Steers a predictable course but does deliver mild thrills along the way.