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When a genetic experiment so risky it must be conducted in outer space goes awry, Dwayne “The Rock” Johnson hurries to save his friend, the extraordinarily intelligent silverback gorilla George, from leveling the city of Chicago. That’s the gist of “Rampage,” the new dumb-fun actioner reteaming Johnson with his “San Andreas” director Brad Peyton. It’s another save-the-world vehicle for Johnson, who again exploits a charisma as big as his biceps. The plot — a trio of animals grow into massive monsters and lay the smack down — is preposterous. But Johnson, as primatologist Davis Okoye, head monkey-whisperer at the San Diego Wildlife Sanctuary, doesn’t let a limp script laden with junk science and inane dialogue ruin his good time — or ours.

Somehow it took four writers to cobble together this lumbering adaptation of a video game, but the cast — from Johnson on down to the CGI-d beasts — makes a silk purse out of a gorilla’s ear. Johnson and George are hands down the year’s best screen couple. They knuckle up, flip each other off and communicate through sign language and gesture. Call it an interspecies bromance.

Naomie Harris (“Moonlight”) plays an ax-grinding, disgraced scientist inserting herself into Davis’ attempts to transform George back into the gentle ape he rescued from poachers when he was an Army Ranger. Jeffrey Dean Morgan, from TV’s “The Walking Dead,” is a government agent knocking heads with Johnson. Whenever they share the screen, the two he-men project some serious swagger. The jury is still out on whose smile is more magnetic.

Malin Akerman (“Billions”) is a hoot as campy villainess Claire Wyden. Her mutagenic serum causes rapid growth and induces rage in the three rampaging beasts: Gorilla (George), reptile (Lizzie), and wolf (Ralph). Jake Lacy (“Obvious Child”) plays Claire’s doltish brother. Rounding out the cast are Joe Manganiello’s (“Magic Mike”) animal-killer-for-hire and Demetrius Grosse (“Straight Outta Compton”) as the Army colonel tasked with taking down the three supersized animals deemed “weapons of mass destruction.”

Peyton really knows his way around disaster movies — and epic character demises. He dials up an abundance of critter carnage, plane crashes, crumbling skyscrapers, and a multitude of bullets, bombs and missiles. He blows stuff up so good — often defying the laws of physics and gravity — you forgive his want to completely abandon characters (P.J. Byrne, Breanne Hill, Jack Quaid) introduced early in the movie. Byrne is pretty funny in his limited part. I would have liked more of him. Peyton also struggles with tone. He’s serious one minute, cheeky the next. It’s a hard line to toe, but he’s lucky Johnson is leading the charge. Nothing beats seeing the big guy monkeying around.

— Dana Barbuto may be reached at dbarbuto@ledger.com or follow her on Twitter @dbarbuto_Ledger.

“Rampage”
Cast: Dwayne Johnson, Jeffrey Dean Morgan, Naomie Harris, Malin Akerman, Jake Lacy, Joe Manganiello.
(PG-13 for sequences of violence, action and destruction, brief language, and crude gestures.)
Grade: B+