The fact that I can’t remember much about Chris Columbus’ 2010 “Percy Jackson and The Olympians: The Lightning Thief” (based on the young-adult book series by Rick Riordan) isn’t exactly a good sign. Even when I read through the plot synopsis, my mind went blank.

It also isn’t a good sign that the sequel, “Percy Jackson: Sea of Monsters” (directed by Thor Freudenthal) came out two years after the first one and in August.

You’d think that if 20th Century Fox had a lot of faith in this “Harry Potter” knockoff (instead of wizardry and magic, it’s Greek mythology), it would have made the sequel right after the first one and released it in prime summer-movie time, in June or July.

With all that considered, it’s not like I went into “Sea of Monsters” with high expectations, but I thought it could be, at the very least, an entertaining and funny fantasy movie. Plus, it has “The Perks of Being A Wallflower” star Logan Lerman in the title role of Percy Jackson (a regular teenager who finds out he’s the son of Poseidon), and he’s proved himself to be legitimate actor capable of carrying a movie.

But, alas, this film shows that “Percy Jackson” is destined to be nothing more than a C-grade “Harry Potter” knockoff.

“Sea of Monsters” is a miserable attempt at capitalizing on a young-adult book series and earning box-office dollars. Marc Guggenheim’s screenplay fails to craft an interesting story and create convincing characters and relies too heavily on its Greek-mythology hook.

Following the events of the first movie, young Percy now lives at Camp Half Blood, a secret camp deep in the woods where all of the young demigods (half-god, half-human) can live in peace. After saving the world the first time around, Jackson is in a bit of a sophomore slump. He’s worried he’s going to be a one-quest wonder, even though there’s a prophecy (there’s always one) that says he’s going to do great things.

Anyhow, the safety and tranquility of Camp Half Blood is threatened when the special tree (don’t ask) that creates a protective barrier around the camp is dying. So Jackson and his two friends, Annabeth (Alexandra Daddario) and Grover (Brandon T. Jackson), embark on a quest suspiciously like “The Odyssey” to retrieve the legendary Golden Fleece to save the tree.

If that storyline isn’t riveting enough for you, there’s also a subplot involving the character of Tyson (Douglas Smith), Jackson’s half-brother and the newest resident of Camp Half Blood, who comes along with them. And get this: Tyson is an ugly Cyclops so, of course, he’s the bumbling, outcast, freak who messes everything up and has to prove his worth to his attractive, teen, demigod comrades.

Annabeth is particularly nasty to him and takes every opportunity she can to talk down to him — a real positive message being sent to the kids in the audience.

There’s also demigod Luke (Jake Abel) the son of Zeus, who wants the Golden Fleece for himself so he can bring back Cronos from the dead to destroy Mount Olympus.

After the quick setup and the demigods embark on their epic journey, the movie becomes one boring action set piece after another, and it plays out exactly how you’d expect it to.

The film also tries too hard to be funny: Every line of dialogue feels forced and almost sitcom-y. An especially terrible example comes toward the end when Percy and his lads are tied up and Percy cut Grover’s hands free. Grover says, “Hey, don’t cut off my hands! I’m kind of attached to them.”

The sad part is that I could probably overlook some of this if the characters were just a little better, but they’re all either one-note or have little or no reason to be there. Percy is just your typical, mopey “chosen boy” with a case of the chosen-one blues who doesn’t think he’s capable of saving the world again. Lerman’s talent is practically wasted in the role.

As for the supporters: Grover is there to provide comic relief (although he doesn’t do a very good job), and Annabeth is there because a female friend is needed for the hero. But the fact that she’s so mean and disgusting toward Tyson makes her annoying. As for Luke? Well, Voldemort, he ain’t. I don’t think I’ve seen a more bland and forgettable movie villain this entire year.

I realize I haven’t read any of the books but I shouldn’t need to. A movie needs to build strong characters and tell a compelling story on its own, and “Percy Jackson: Sea of Monsters” doesn’t even come remotely close to doing that.

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