Any thoughts that a second Percy Jackson and the Olympians film would drag Rick Riordan’s “Greek Godchildren” franchise out of the shadow of Harry Potter are dashed the moment Percy and his “half-blood” friends pile into a supernatural taxi in “Sea of Monsters.”

The cab may be driven by the three haggling, wisecracking Graeae of Greek myth – blind women with one eye between them — but it’s a pure Potter picture moment.

And with every magical creature that turns up, which one of these half-human sons and daughters of Poseidon or Athena then identifies — “Look, it’s a Hippocampi!” “Oh no! It’s a Charybdis!” — the comparisons to Harry & Co. grows.

But “Percy Jackson: Sea of Monsters,” the sequel to “The Lightning Thief,” is never less than a workmanlike and likable substitute for kids who like their entertainment magical. Good effects, an adequate young cast (Logan Lerman, Alexandra Daddario and Brandon T. Jackson return) and the amusing presence of Stanley Tucci and Nathan Fillion lift this otherwise warmed-over myth mush movie.

A prologue remembers a death, years ago, at Camp Half-Blood, the woodsy Hogwarts of this mythic world. The brave dead demi-god who sacrificed herself back then lives on as a magical tree that guards the camp from attacks by outsiders. But someone has poisoned the tree.

Percy (Lerman), the kid who saved Olympus last time around, isn’t the first choice to save it now. He’s outclassed by the sporty, trash-talking Clarisse (Leven Rambin). Clarisse is given the job of fetching a cure for the tree – the Golden Fleece, the same talisman Jason and the Argonauts once sought. But Percy, Annabeth (Daddario) and the Satyr Grover (Jackson) sneak off on a quest of their own to see if they’re the ones destined to fetch the fleece and save Olympus. Again.

They’re joined by Percy’s dorky new half-brother, Tyson (Douglas Smith). Tyson is a Cyclops, you know, the one-eyed fellows who gave Odysseus so much trouble in “The Odyssey.” The one-eyed kid is accident prone, a screwup.

“Is it your lack of depth perception, maybe?”

The movie starts out promisingly with the comical introduction of camp guru “Mr. D,” Dionysus, the witty Greek god of wine. Stanley Tucci is hilarious in the part, a god who loves his vino but is being punished by Zeus so every vintage bottle he opens with care turns to water in his glass.

“You know, the Christians have a guy who can do this in REVERSE. Now THAT’s a god!”

The always amusing Nathan Fillion shows up, running a UPS store as Hermes, father of the villainous Luke (Jake Abel) whom we thought Percy had disposed of in the first film but who is back and striving to end the world. Again. Not to worry, says Hermes.

“Rome wasn’t built in a day. Take it from me, I was there.”

That gets at the central failing in this film. There’s no life-and-death weight to it, no “Cedric Diggory’s dead and we can’t bring him back” moment aside from that opening tree-girl flashback.

The quest, which takes our heroes to the Sea of Monsters, aka The Bermuda Triangle, is generic in the extreme. The fights/escapes all lack any sense of urgency and peril.

The first Percy Jackson movie wasn’t a blockbuster and yet this one sets us up for further adventures with these 20something teenagers and their training camp. But until they have the guts to kill somebody, to give us a real sense that there’s something truly at stake, why should we invest in it?