2010's "Percy Jackson & the Olympians: The Lightning Thief" was a solid family-targeted adventure with an unforced educational bent dipped in ancient Greek mythology. Based upon the first young adult novel in a series of five by Rick Riordan, the movie did only okay business in the U.S., earning $88-million on a $95-million budget, but was more popular overseas. With the cumulative box-office take helping the project break even and then some, 20th Century Fox has seen fit to adapt Riordan's second book for the big screen. Coming to theaters a long three-and-a-half years later, "Percy Jackson: Sea of Monsters" is the clear-cut product of a studio fearful of taking chances and spending the money necessary to stand confidently alongside its predecessor. Certainly a film's cost has nothing to do with how good a film is, but the whole enterprise this time suffers from being blatantly chintzy and regrettably bland, the location shooting of the first picture swapped for studio backlots and the original A-list adult cast either discarded (e.g., Steve Coogan, Rosario Dawson, Catherine Keener, Sean Bean, Uma Thurman) or replaced by more cost-effective actors (Anthony Stewart Head takes over for Pierce Brosnan as Centaurian Half-Blood activities director Chiron). The drop in quality and care is kind of a bummer.

When adolescent Half-Bloods—that is, half-human, half-Gods—Annabeth (Alexandra Daddario), Grover (Brandon T. Jackson) and Luke (Jake Abel) were children, their journey to seek protection at Camp Half-Blood was met with tragedy when their friend, Thalia (Katelyn Mager), was killed trying to defend them against a rampaging Minotaur. In her death, a magical pine tree sprouted from the ground, creating a protective barrier between the regular world and the camp. It is this very shield that is suddenly threatened years later after the tree is poisoned, the property suddenly vulnerable against invading monsters. Star classmate Clarissa (Leven Rambin) is sent on a quest to capture the Golden Fleece, the sole object with the powers to heal the tree, and right behind her are Percy Jackson (Logan Lerman), son of Poseidon, best friends Annabeth and Grover, and Percy's newly discovered brother, Tyson (Douglas Smith), a one-eyed, half-God/half-sea nymph who yearns to fit in. As Percy comes into his own as the natural leader he has doubted himself to be, their perilous mission will take them from Washington, D.C. to the Bermuda Triangle to an abandoned amusement park on the island of the Sirens, where they will have to face off against the mighty Kronos.

"Percy Jackson: Sea of Monsters" follows a very similar narrative structure as "The Lightning Thief," the bulk of the story dedicated to a scavenger hunt-like expedition that Percy and his buddies must go on in order to save loved ones and prove their mettle as warriors. Taking over for director Chris Columbus is Thor Freudenthal (2010's "Diary of a Wimpy Kid"), and succeeding Craig Titley on scripting duties is Marc Guggenheim (2011's "Green Lantern"). It is difficult to say if the change in talent is the main reason why "Percy Jackson: Sea of Monsters" comes off as a low-rent follow-up, but trouble is most definitely afoot. More often than not, Percy and the gang look as if they're running around in front of a green screen, a result of deficient effects work. When they travel to the nation's capital, their surroundings are so unconvincing that they might as well be in Scranton rather than the District of Columbia. When out on the high seas, the depth of the background looks less like an ocean's horizon and more like they're about to row right into the wall of the soundstage. A major motion picture in 2013 has no excuse looking so cheap, and not even the few halfway impressive shots, such as a vortex our heroes get caught in and another moment where the tail of a creature appears behind Percy and Annabeth as they chat below deck, can make up for it.

Logan Lerman brings a valiant conviction to the title role of Percy Jackson, but he must have sensed this particular project was a step down from 2012's "The Perks of Being a Wallflower," one of the definitive motion pictures about teenagers in recent years. By comparison, this is just malarkey, not even worth the underlying learning pleasures of "The Lightning Thief" and egregiously missing much of the spirit of the original. The absence of Catherine Keener, as Percy's caring mother, is especially felt; without that core relationship that gave Percy's circumstances a certain levity and heart, the film feels hollow. The rest of the cast is fine, but they are all at the mercy of having to act against gods and giants and monsters that aren't really there while getting minimal chance to better explore their characters. Never in the film is it mentioned how much time has passed between the events of the previous movie and this one; both feel self-contained and not really pieces of a bigger story the way the "Harry Potter" series always was.

Here is some free side advice to the creators of "Percy Jackson: Sea of Monsters:" when your story takes your protagonists to an eerie, derelict amusement park (one of the few locations that looks like a genuine place rather than the work of poorly defined CGI), take advantage of the setting! When the characters hop aboard a foreboding ride called Plummet of Death, the viewer anxiously awaits for a thrilling payoff that instead comes to a hasty anticlimax when the coaster's track arrives at a dead end of falling rocks before they've so much as gone down a single drop. The scene is nothing if not a cruel joke, followed thereafter with some cornball business involving a kidnapped Grover posing as a chambermaid to appease a Cyclops. "Wait, you're a dude?" the Cyclops remarks in disbelief when the truth is revealed. Climactic fight scenes ensue soon thereafter and the day is more or less saved, but then director Thor Freudenthal chooses to end things on a wobbly cliffhanger when chances of a second sequel actually happening are far from a sure thing. The ending voiceover delivered by Percy is so ham-fisted it's a wonder the fade to black doesn't come with a "BUM-BUM-BUM-BUMMM!" striking of a piano. "Percy Jackson: Sea of Monsters" is less evocative of a big summer movie than a "Choose Your Own Adventure" book. Sure, it might be pleasurable off and on, but that doesn't take away how junky and inconsequential it is as a story.