When a terrible movie like 2010’s “Clash of the Titans” grosses $493 million worldwide, why bother making a good sequel?

That may have been the thinking behind “Wrath of the Titans,” an inept film set 10 years after the first chapter, during which the Greeks have lost interest in their gods and Perseus’ son is now an audience-friendly 10-year-old.

Like many a retired action hero before him, the demigod Perseus (Sam Worthington) must leave his quiet fishing village and his son, Helius (John Bell), to save his father, Zeus (Liam Neeson), who has been imprisoned by Uncle Hades (Ralph Fiennes).

Hades, meanwhile, has unleashed upon the world their imprisoned father Kronos, leader of the Titans.

Because a lone demigod can’t defeat a god (but two can), Perseus flies off on Pegasus to pick up Poseidon’s son Agenor (Toby Kebbell), a dreadlocked lowlife imprisoned in the jail of Queen Andromeda (Rosamund Pike). Together they set sail for the island home of Hephaestus (Bill Nighy), the half-mad architect of Zeus’ underworld prison who is long used to conversing only with his mechanical owl Bobo.

As in a video game, Perseus also must acquire three weapons — Zeus’ thunderbolt, Poseidon’s trident and Hades’ pitchfork — all of which conveniently shrink down for portability. Like a kid in a toy commercial, Helius cries, “The Spear of Triam!” when they’re assembled into one.

The plot acknowledges Worthington’s recessive presence by minimizing his screen time. No longer coasting on “Avatar” fumes, he is now merely a pleasant-looking Aussie who got lucky. While Neeson and Fiennes face off, comic relief is provided by Nighy and Kebbell, who acts like he’s subbing for Russell Brand.

Pike, an actress of uncommon warmth, is preposterous as a warrior queen, and Edgar Ramirez, as the snarling god of war Ares, is dreadful. Alliances shift with little motivation, and when the going gets dismal the writers throw in another “Release the Kraken!” joke.

The climax offers dual-torsoed, six-armed soldiers that would do creature-feature icon Ray Harryhausen proud, but the rest you’ve seen many times before, and better. The bargain-basement effects seem intended to remind the audience that director Jonathan Liebesman helmed “Battle Los Angeles.”

“Wrath of the Titans” is rated PG-13 for “intense sequences of fantasy violence and action,” although boys Helius’ age are the only ones likely to enjoy this.

What others are saying

•  Roger Moore, McClatchy-Tribune: “The screenwriters give it a lighter touch, a bit of mythic whimsy amongst all the muddle. Director Jonathan Liebesman and company keep this stripped down (few gods, not too much dialogue) and manage a few surprises and a little fun on the trip.” —

•  Helen O’Hara, Empire: “If even a tenth of the care and attention lavished on the production design and action sequences had been afforded the script, this could have been an adventure of legendary proportions.”

•  Todd McCarthy, The Hollywood Reporter: “As most of the dialogue is shouted or bellowed, it’s rather beside the point to speak of the performances, other than to say that Sam Worthington looked marginally more at home on Pandora than he does in the Greece of myth.”