“You know this story,” the sidekick soon-to-be-known as Igor narrates. Lightning, corpses, “a mad genius.”

But what if you didn’t? You know, “know the story”?

“Victor Frankenstein” is a madcap mashup of three stories — at least as they’re traditionally adapted for the screen — a re-introduction of Mary Shelley’s “Frankenstein” in a world that has seen Disney’s “Hunchback of Notre Dame” and the Robert Downey Jr. “Sherlock Holmes” movies.

And for about 30 sem-frenetic minutes, it works. No, hear me out.

Daniel Radcliffe is a hunchbacked mid-Victorian Era circus freak who pines for the aerielist Lorelei (Jessica Brown Findlay, Lady Sybil on “Downton Abbey”). Whatever his lot in life, this bright young man doubles as the circus medic. And when Lorelei takes a fall, he springs into action.

A cocky passing med student, played by James McAvoy, helps. They “see” the body the same way — through book-learning and training, muscles and ligaments and bones underneath the flesh. The med student frees — literally — the “freak.”

“You’re not a clown, you’re a physician!”

The med student — Victor Frankenstein — has his sidekick. He gives him the name “Igor,” gives him a makeover (a hunchback “cure”), and despite the younger man’s occasional call of “Master,” treats him as his colleague. They will use science and cadavers to make history!

Here’s what we’re to go along with — two of Britain’s most adorable and adored acting exports, in ’80s hair metal coiffures, engaging in staccato banter as they set out to prove that “death can be made a temporary condition!”

In the stunningly-recreated Victorian England here, anything seemed possible.

There’s a crucifix-packing Scotland Yard detective (Andrew Scott) who smells the “roots of an evil, sinful mischief.” And a disapproving Frankenstein-the-elder (Charles Dance, fatherly menace incarnate).

The “science” is a series of grotesque — OK, gross — fleshy experiments, all leading to exactly what we expect.

Treat the whole thing as a vamp and it kind of works. That first half hour of “makeover” crackles with as much wit as scripter Max “American Ultra” Landis can give it.

Alas, the film goes flat as it reaches for the familiar story beats and we realize that all we can recall from director Paul McGuigan’s “Lucky Number Slevin” is its overdose of production design.

Still, those who adore the two stars will find some fun here. And if you don’t “know the story,” you won’t be nearly as bored as the rest of us.

MPAA Rating:PG-13 for macabre images, violence and a sequence of destruction

Cast: Daniel Radcliffe, James McAvoy, Jessica Brown Findlay, Charles Dance, Andrew Scott
Credits: Directed by Paul McGuigan, script by Max Landis. A 20th Century Fox release.

Running time: 1:49