We have just enough time to settle in for the fun ride that “Jungle Cruise” might have been before the rug is almost wholly pulled out from under us.

Dwayne Johnson turns up the charm and charisma as everybody’s favorite theme park ride skipper, Capt. Frank Wolff. He’s a con artist, but “It’s only a scam if you fall for it.” He’s a smart aleck tour guide — “We know that of all the jungle cruises you could have taken….ours was the cheapest.” He’s entirely too fond of puns. “I used to work in an orange juice factory…But I got canned.”

And those go over with the tourists as well as they ever have.

“Mommy, please make him stop.“

Johnson has unexpectedly effortless chemistry with Emily Blunt, who plays Lily Houghton, a somewhat swashbuckling, ever-so-English scientist/researcher who wants to hire him to search for this enchanted Amazonian tree with healing powers.

“If you’re a believer in legends, you should believe in curses, too,” he warns her. “Is there a single thing about you I can trust?” she wants to know.

Paul Giamatti is introduced as an upriver monopolist and threat to Capt. Frank’s tour boat trade, Jesse Plemons makes a perfectly fleshy-faced Teutonic villain, a German prince also looking for a Tree of Life, one possessing “The Tears of the Moon” — blooms which can heal most anything.

Something like that could come in handy in pre-penicillin 1916, in the middle of World War I.

When the formidable Édgar Ramírez (“Point Break,” “Hands of Stone, “Yes Day”) as a supernatural Spanish conquistador, shows up, we go along with it, all part of the “African Queen/Pirates of the Caribbean” mashup that’s being served up. He’s got the Javier Bardem/Bill Nighy role.

But at some point, director Jaume Collet-Serra (“The Orphan,” “House of Wax”) remembers he’s not Spielberg, who made “Raiders of the Lost Ark” after “Sugarland Express and after “1941.” He’s not Gore Verbinski, fresh off the glorious farce “Mouse Hunt” when he launched “Pirates of the Caribbean.”

This “African Queen/Pirates/Raiders” romp, with all its light “Romancing the Stone” potential, goes dark and violent and CGI production-designed to death. Collet-Serra plays up the script’s “Aguirre, The Wrath of God” elements and utterly loses the thread. In punning terms, the “jungle” gets the better of him.

“Jungle Cruise” is a gorgeous-looking lark, with teeming jungles, towering waterfalls, a half-sized German U-Boat and a “cruise” boat — La Quila — that looks like the zombie African Queen.

Lily Houghton brings along her fey fop of a brother MacGregor (Jack Whitehall) who “comes out,” something of a first for a Disney family action film. We get our first gay double-entendre from him, and a less printable second.

“Gosh, there’s certainly a lot of you, isn’t there?”

And we’re treated to a spirited sail up river (and yet “down” rapids) towards the corner of Amazonia that legend says was home to this magical tree, with shifty Capt. Frank repeating “You’re gonna BEG me to turn back” and labeling the first woman of science he’s ever met as “Pants,” thanks to her attire.

As her hired captain, he’s just “Skippy” to her.

Giamatti may mostly be lost in the story early on, but there’s enough nonsense to atone for that.

Still, the digital snakes, toucans and piranhas — “Better eat them before they eat you!” — are joined by Capt. Frank’s half-convincing digital jaguar, something of a let-down.

The jokes wane and the tone darkens and the charm just drains straight out of “Jungle Cruise.”

Collet-Serra spoils a bravura opening, with Blunt giving us a taste of Johnny Depp/Orlando Bloom derring do as Lily tricks the sexist, dismissive Royal Society out of its map of that jungle she wants to cruise to find that tree she insists really exists.

He wastes Johnson summoning up decades and decades of Disney Jungle Cruise theme-park ride nostalgia — the puns, the wisecracks, the dire warnings — “Everything you see wants to kill you, and can.”

It’s a film that wants to be a little of this, a lot of that and funny in the bargain. You want to like it so much that you can sense Disney getting a new franchise out of it, even if it doesn’t quite come off. But if they do sequels, they’d bloody well better hire somebody who knows comedy to film them.

MPA Rating: PG-13 for sequences of adventure violence

Cast: Dwayne Johnson, Emily Blunt, Paul Giamatti, Jesse Plemons, Jack Whitehall,
Veronica Falcón and Édgar Ramírez.

Credits: Directed by Jaume Collet-Serra, script by Glenn Ficara and John Requa. A Walt Disney release.

Running time: 2:07