The third time around isn’t the charm for this series based on C.S. Lewis’ “Narnia” books, which dispensed Christian messages to young readers in the seven volumes he produced between 1950 and 1956. “The Voyage of the Dawn Treader” sees a change in the director’s chair, with Andrew Adamson limiting himself to a producing credit after co-writing and helming the initial two installments. But his replacement, veteran Michael Apted, proves no more capable than he was in engendering much visceral energy into the proceedings. Like the earlier pictures, this one is visually opulent, but episodic and, despite all the action, oddly tame and lethargic.

This time around, the older of the four Pevensie children who traveled to the magic realm of Narnia in the first two films—Peter (William Moseley) and Susan (Anna Popplewell) are absent apart from a few inserts; they’re off in America with their parents, while their younger siblings Edmund (Skander Keynes) and Lucy (Georgie Henley) are stuck back in England rooming with their aunt, uncle and dreadful little cousin Eustace ( Will Poulter, whom you might remember from “Son of Rambow”).

But a picture of a ship on the sea on the wall of the guest room miraculously takes the three children into the realm of Narnia, where they’re picked out of the drink by Prince Caspian (Ben Barnes, looking a lot better than in the previous picture with his hair cut short). He’s on an expedition in search of the seven lost lords of Narnia, who disappeared years earlier, each with one of seven powerful swords, after Caspian’s father was overthrown. The children join in the search, Edmund and Lucy with enthusiasm and Eustace, the unbeliever, great reluctance, and go through a series of adventures that bring them into contact with a gang of slave-traders, a magician and a band of one-legged elves he’s made invisible, and a vicious sea monster as they make their way to a dark island. In the process their mission becomes the recovery of the seven swords and their placement on the table of the lion Aslan (voiced by Liam Neeson)—an act that will liberate the land from evil and restore its lost purity.

In the course of their journey, all the human characters—Caspian, Edmund and Lucy—must resist temptation. But this “Voyage” is really Eustace’s story. He represents the soul without faith that’s redeemed through Aslan’s intervention. At one point Eustace’s greed turns him literally into a dragon. But by proving his courage in the face of evil, and accepting Aslan’s help, Eustace is saved. And he develops a deep friendship with Reepicheep (voiced by Simon Pegg), the endlessly courageous talking rat swordsman, who becomes the only character that enters the Aslan’s country—heaven, of course—at the end.

The religious meanings are constant throughout “Dawn Treader,” but that’s not the problem with the film—they’re not oppressive except in the material involving Aslan (as when he pointedly tells Edmund and Lucy that they must come to know him under another name in the real world). It’s rather that the movie has a lackadaisical feel, with the action seemingly secondary to the admittedly good special effects; it looks fine, but simply lacks energy. (Even the sequences involving the dragon and sea serpent come across as tepid.) Part of the cause rests in the performances—apart from Poulter, they lack vitality—but much of the blame rests with Apted, whose “7 Up” series remains one of the masterpieces of documentary filmmaking but whose fiction films have been wildly uneven. This is not one of his more successful efforts; handsome but rather dull, it hearkens back to the Ray Harryhausen “Sinbad” pictures that were exciting in the fifties and sixties but feel very tame to younger viewers today.

There’s one more big change from the previous “Narnia” pictures here. “Dawn Treader” is being released by Fox, after Disney, which distributed the “The Lion, the Witch and the Wardrobe” and “Prince Caspian,” declined to continue its association with Walden in making the series. Fox has long been searching for a young people’s franchise, but it’s doubtful this one will prove a bonanza. And though two of the remaining books (“The Silver Chair” and “The Last Battle”) feature Eustace, it seems unlikely that either of them could serve for another sequel. “Narnia” fans will probably have to be satisfied with a trilogy that frankly hasn’t been all that satisfying.