Was Catholic novelist Tim Powers’ 1987 historical fantasy-adventure novel On Stranger Tides in some way the inspiration, or an inspiration, not only for this fourth Pirates of the Caribbean flick, but for the whole Pirates franchise?

Powers’ fans noted striking connections eight years ago, when The Curse of the Black Pearl made its debut: Like the novel, there were sailors’ tales about a dreaded pirate ship crewed by the undead and glimpsed only at night and an impoverished hero forced to turn pirate in order to save a heroine — named Elizabeth — who has been kidnapped by pirates. Powers’ novel even featured a boozy hero named Captain Jack S. (not Sparrow, but a different two-syllable name, Shandy) who gets drunk on the beach — though Johnny Depp’s character is entirely his own creation. (Wikipedia articles suggest further entanglements.)

While Disney certainly wouldn’t acknowledge any influence on the series from the outset, they did option Powers’ book a number of years ago for a possible sequel — and now here is Pirates of the Caribbean: On Stranger Tides, with the cagey credit line: “Suggested by the novel by Tim Powers.” Powers fans, take note of that modest verb. The filmmakers have borrowed the title and a few key concepts, like a voodoo-wielding Blackbeard and the Fountain of Youth, but On Stranger Tides is a Pirates of the Caribbean sequel, no more, no less. Especially no more.

Both the impoverished hero played by Orlando Bloom and Keira Knightley’s Elizabeth are gone. With them are nearly all the rest of the crew from the earlier films, including three-time director Gore Verbinski, who has been succeeded by Rob Marshall (Chicago). Only those old antagonists, Jack Sparrow and Hector Barbossa (Geoffrey Rush), are left to soldier on, along with first mate Mr. Gibbs (Kevin McNally).

Newcomers include Ian McShane as legendary pirate Blackbeard and Penelope Cruz as Angelica, a pirate’s daughter, pirate’s lover and pirate in her own right. Is it all pirates, all the time? Well, there’s also an earnest missionary, Philip Swift (Sam Claflin), and a soulful mermaid, Syrena (Àstrid Bergès-Frisbey). But neither is developed as a character, so, for the most part, On Stranger Tides is steadfastly a tale of pirates jostling with other pirates: Sparrow vs. Angelica; Sparrow vs. Barbossa; Barbossa vs. Blackbeard; Sparrow vs. Blackbeard, and so on.

What this exercise establishes is that while everyone loves Han Solo, it turns out you need Luke and Leia, too. Playing straight man to Depp’s Captain Jack, as Bloom did through at least a movie and a half, may have been a thankless task — but without Bloom to goad and mock, and without Elizabeth to flirt with and discomfit, Sparrow’s roguish schtick palls. Flirting with Angelica isn’t the same, because she’s a pirate and isn’t discomfited in the same way. How funny would Groucho’s impudence be if Margaret Dumont came back at him like Mae West? How amusing would Astaire’s insouciance be if Ginger didn’t at least pretend to be offended?

To compensate for this lack of tension, On Stranger Tides dials up the innuendo and sensuality. Sparrow and Angelica roll around on the deck of the Queen Anne’s Revenge, and Angelica, who shows some religious feeling, accuses Jack of debauching her in a convent where she was set to take her vows. Jack protests that he mistook the convent for a brothel and indicates in so many words that Angelica was too accomplished to have been as innocent as she purports. Boo.

The movie gets off to a limp start due to a precedent established in previous films: making Sparrow’s entrance into the film as outrageous as possible. It was brilliant once and amusing twice, but it’s become a millstone around the franchise’s neck.

Despite this, On Stranger Tides is ultimately an improvement on its predecessor, the bloated, misconceived threequel At World’s End. There are a few nicely staged action sequences, notably a chase sequence in the streets of London, that play like homages to Charlie Chaplin by way of Jackie Chan. A bit where Jack escapes from being tied to a palm tree recalls the Looney Tunes’ logic just as his shishkebob pole-vaulting routine from Dead Man’s Chest.

A sequence set aboard a ruined ship inexplicably balanced on the edge of a cliff is inspired by the famous tipping shack sequence in Chaplin’s Gold Rush, but fails because we never really get a sense of the physics of which way the ship is tipping and why. And there’s a nice gravity-defying conceit at the Fountain of Youth that recalls the best bit in At World’s End, the ship-inverting logic for escaping from Davy Jones’ locker, and also, very slightly, the wood between the worlds in C. S. Lewis’ The Magician’s Nephew.

The movie fleetingly invokes Catholic–Protestant tensions: The kings of England and Spain both send expeditions in search of the Fountain of Youth, and George II of England is furious at the thought of the fountain winding up in Catholic hands. When the Spanish turn up, they proceed to shoot an Englishman in cold blood before commending his fortitude — then reveal unexpectedly zealous religious motivations. Whether their actions are fanatical or reasonable is actually kind of an interesting question. Maybe the only interesting question in the movie, since I can’t think of any others.

Swift, the missionary, isn’t integral to the plot, but his presence does juice the odd religious themes running through the earlier sequels. For once, a devout Christian character is positively depicted, if not in any depth, in a mainstream Hollywood film. What’s more, the other characters generally respect his piety — even Blackbeard, whose soul Swift wants to save, though the missionary admits it’s a long shot.

When we meet Swift, he’s been lashed high to the mast by Blackbeard. During a mutiny, a pirate threatens Swift: “You’re either with us or against us!” When Swift demurs — “I’m neither with you nor against you!” — the pirate looks uncertainly at Sparrow, asking doubtfully, “Can he do that?” Sparrow’s knowing reply: “He’s religious. I think it’s required.” I like that.

When the pirates capture one of a fierce, seductive school of mermaids — a mermaid is needed for a ritual at the Fountain of Youth — Swift takes pity on her and does what he can, which is not much, to ensure that no mermaids are harmed in the making of this film. He even gives her a name, Syrena, which sounds like Serena (meaning “serene” or “calm”) but is Spanish for “mermaid” (compare “siren”). (Coincidentally, Serena is Powers’ wife’s name.)

When Syrena’s demurely draped hair is no longer sufficient to preserve her modesty and the film’s PG-13 rating, Swift lends her his shirt, in the process establishing that missionaries can be buff. Whether Swift is ultimately a heroic character or a sucker may depend on the sequels. I can’t say it will bother me if I never find out.

Register film critic Steven D. Greydanus blogs at NCRegister.com.

Content advisory: Intense action violence and menace; some frightening images; partial nudity (nothing explicit), sensuality and recurring innuendo. Teens and up.