Percy Jackson (Logan Lerman) engages in a fiery battle. Photo by Murray Close/20th Century Fox Film Corp.

It’s been more than three years since Percy Jackson & the Olympians: The Lightning Thief, the first film installment of Rick Riordan’s ultra-popular “Percy Jackson and the Olympians” series (Hyperion) jumped onto the screen. The half-blood (or demigod) Percy, son of the omnipresent but unseen Poseidon, takes off on another adventure in this visual equivalent of a loud and boisterous amusement ride. In Sea of Monsters, the 17-year-old (Logan Lerman) wants to prove that he’s not a “one-quest wonder,” but this movie franchise-wannabe doesn’t escape that dig. The first film, directed by Chris Columbus, had a tongue-in-cheek sense of humor, especially in the teen’s interactions in the real world and his reaction to his very ancient lineage. Ironically, by taking place in a world of monsters and angry gods, Percy comes off as more ordinary this time around. To recall the back story, viewers might want to have read the source material (or be up on your Greek mythology). Regardless, moviegoers won’t get confused. The characters are basic stock figures: the kid next door; the hapless comic relief of Grover (Brandon T. Jackson), a satyr from the waist down; and the know-it-all Annabeth (Alexandra Daddario), daughter of Athena. No, you’re not experiencing déjà vu. There are plenty of obvious comparisons to the “Harry Potter” series.

Percy Jackson and Annabeth (Alexandra Daddario). Photo courtesy of 20th Century Fox Film Corp.

The movie’s story has been “a millennium in the making,” as one character intones. Someone, or something, wants to invade and annihilate Camp Half-Blood where Percy and his peers are heroes-in-training. The camp’s protective giant tree has been poisoned, and a bronze bull has been on the attack, so the three sneak out, along with Tyson (Douglas Smith), a Cyclops and Percy’s half-brother, in search of the Golden Fleece, which heals anyone or anything. The fabric has been held hostage by the Cyclops Polyphemus on an island in the middle of the Sea of Monsters, better known as the Bermuda Triangle. Along the way, Hermes (Nathan Fillion) hams it up, and Cronus makes a catastrophic cameo. (Incidentally, Percy is not the only one with distant deity daddy issues.) The trio’s journey makes the Maze of the Minotaur seem fairly straightforward, and a list of the plot differences between the book and movie would be as long as any web Arachne could weave. (A chariot race, a Pegasus, and Tantalus are among those missing in action.) Everyone is fluent in movie-speak, as in Hermes’ advice to Percy, “One thing I’ve learned in three thousand years, don’t give up on family;” or when the main villain threatens, “The Olympians who scorned us will know death.” Percy also gets into the act: “I make my own destiny.” But like the book, the saga moves at a clipped, out-of-breath pace, and the work of the 3D special effects team adds a jolt of energy when the creepy and cranky creatures are on the rampage.

Photo courtesy of 20th Century Fox Film Corp.

In the books, Percy has to figure out what to do or how to solve the meaning of his many premonitions. On screen, he and his cohorts are more reactive, pawns of the gods, really. They are quick on their feet, but none of them have special powers or abilities except for what has been given to them by the Olympians, like a mystical tape gun or a ball-point pen that turns into a retractable sword. Percy is even told the coordinates to find the island. How can Percy really be a hero if he is given the devices or is told what to do? He’s not saving the gods, the gods are saving him. Directed by Thor Freudenthal Rated PG 106 min. Opens nationwide August 7.