It's been three years since "Percy Jackson & the Olympians: The Lightning Thief," so a bit of exposition reminds audiences that the Percy (Logan Lerman) is the half-human son of the sea god Poseidon.

When Camp Half-Blood, the teenage demigods' woodsy refuge, is suddenly in peril, Percy and his friends, Grover (Brandon T. Jackson), a satyr, and Annabeth (Alexandra Daddario), daughter of Athena, must retrieve the fabled Golden Fleece from the titular Sea

of Monsters (a.k.a. the Ber-muda Triangle) in order to restore the Camp's protective barrier.

They're joined in this quest by Percy's half-brother Tyson (Douglas Smith), an insecure, sweet-natured Cyclops with one huge CGI eye. Not surprisingly, they're in rivalry with highly competitive, self-centered Clarisse (Leven Rambin), daughter of Ares, who has joined forces with Luke (Jake Abel), the

roguish, resentful son of Hermes. Combative Luke is determined to use the Fleece's restorative powers to resurrect evil Cronos, the vengeful Titan who was vanquished centuries ago.

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Based on Rick Riordan's young adult books, it's formulaically adapted by Marc Guggenheim ("Green Lantern") and awkwardly directed by Thor Freudenthal ("The Diary of a Wimpy Kid"), who has recast Stanley Tucci as wine-loving Dionysus, the frustrated camp director; Anthony Head as the centaur Chiron; and Nathan Fillion as Hermes, god of travelers, messengers and thieves, now serving as manager of a UPS store. Missing are Sean Bean, Kevin McKidd and Steve Coogan as Olympian brothers Zeus, Poseidon and Hades.

This is the kind of visual adventure popularized, years ago, by animator Ray Harryhausen. Converted to 3-D in post-production, the most notable special effects include the fire-breathing Colchis Bull, a supernatural taxi ride with three haggling Graeae (Missi Pyle, Yvette Nicole Brown, Mary Birdsong), a sea-faring jaunt aboard a Hippocampus and a climactic battle with Polyphemus, the Cyclops guarding Circeland, an abandoned amusement park. Problem is: there's little urgency or peril.

On the Granger Movie Gauge of 1 to 10, "Percy Jackson: Sea of Monsters" is a flimsy 5, fantastical fun aimed at preteens familiar with pop-culture Greek mythology.