“IF” is also an acronym in the film for “imaginary friend,” and the movie spurs the audience to consider the impossible: What if our imaginary friends never disappear with time and memory, but remain in the world, purposeless and friendless?

It’s an interesting premise, and Krasinski has leveraged his hefty Hollywood contacts list to contribute voices to the imaginary friends. However, a cute premise and a bunch of stars are pretty much the only things going for “IF,” which is a surprisingly somber film with serious storytelling problems, because Krasinski hasn’t bothered to flesh out the fantastical world-building of his script.

It’s a bit ironic because the characters repeatedly talk about the importance of stories. In an opening narration, our heroine Bea (Cailey Fleming) describes how when she was a child, her mother would ask her for a story; later, she tells a story to her father (Krasinski) in one of the film’s climactic, cathartic moments. Krasinski insists that stories are important but never actually demonstrates why or how. And on a structural level, the storytelling of “IF” itself is a mess: a heartfelt but dramatically inert endeavor that whipsaws between tones ranging from whimsical to morose.

Ryan Reynolds and Cailey Fleming in the movie “IF.”

(Jonny Cournoyer)

This may pretend to be a film about imaginary friends, but what it’s actually about is dead and dying parents. The “IFs” are the coping mechanism, and they are also the emotional tether to childlike wonder and comfort in escapism, which is something that 12-year-old Bea needs more than ever. In an opening montage, we see her happy childhood and her mother (Catharine Daddario) slipping away due to illness. When we meet Bea again in the present, her father is in the hospital with a “broken heart” (though he’s plenty spry enough to pull childish pranks and high jinks).

Bea is staying with her grandmother (Fiona Shaw) in her childhood apartment in Brooklyn Heights, strangely left to her own devices, and ends up falling in with her reticent neighbor Cal (Ryan Reynolds) and his two magical associates, a giant purple guy named Blue (voiced by Steve Carell) and a ballerina Minnie Mouse creature, Blossom (voiced by Phoebe Waller-Bridge).

Blue and Blossom are IFs whose kids have grown up and they’d like to find new ones to befriend. After they explain their plight, Bea takes on the matchmaking task as her new “job.” It’s never explained what will happen to the IFs if they don’t get paired up, as it seems they just go live in a retirement home underneath Coney Island. But Bea seals the deal with a musical performance of Tina Turner’s “You Better Be Good to Me,” which is a callback to her own childhood memories but also feels like an extensive inside joke.

They soon realize that they need to be tracking down the adult pals of the IFs instead of looking for new ones, and so Bea roams New York City with Cal, Blue and Blossom looking for these kids and trying to activate their sense memories so that they can see their IFs again.

There’s a lot of potential disbelief to suspend here. A set of rules and regulations about these imaginary creatures would help. Who can see them? Why does Bea’s grandmother not wonder why she is running off to Coney Island all day? Is her dad in a mental hospital? Is any of this actually happening?

Krasinski emphasizes poignancy over coherence, with composer Michael Giacchino wildly overscoring the piece in order to convey narrative beats that simply aren’t there. The oddly paced film feels randomly strung together, spiced with a collection of one-line vocal cameos delivered by high-profile Krasinski pals (George Clooney, Matt Damon, Maya Rudolph, Emily Blunt, Jon Stewart, Bradley Cooper, Keegan-Michael Key, Sam Rockwell, Awkwafina, Blake Lively, Amy Schumer, Christopher Meloni, Richard Jenkins, etc.). The film looks great, with rich, vintage production design by Jess Gonchor, and it’s beautifully shot by Steven Spielberg’s master cinematographer Janusz Kaminski. But the whole conceit is so undercooked, it could give you salmonella.

“IF” is a film from an adult’s perspective about the importance of imagination, and a reminder to stay connected with our own sense of childlike wonder. But is it a movie for kids, or for the inner child of an adult? With its nonsensical, confounding story, it might not be for anyone, even if its heart is in the right place.