When you get into the back seat of a taxi or Uber or Lyft, you never know what kind of driver you’ll get. Will they be a super-cautious driver or more of a daredevil? Will you sit through the whole ride in silence or will they engage you in conversation?

In “Daddio,” Dakota Johnson is the passenger who gets into Sean Penn’s cab at JFK Airport in New York, headed for West 44th Street between 9th and 10th Avenues. A few minutes go by before Penn, who’s been eyeing her in the rearview mirror, starts asking questions and testing his abilities to figure out what kind of person she is. He quickly sizes her up as a New Yorker, or at least someone who’s lived there for awhile, but he wants to know more. She’s willing to share some things, but not everything.

Since that drive can take at least an hour, and the movie runs 100 minutes, I knew there would have to be some traffic impediment along the way. Sure enough, there’s an accident that stops everyone, giving Penn and Johnson more time for their verbal volleying. But there’s a third unseen character, a man who’s texting with Johnson because he wants to see her — and he’s not shy about it, using some very sexual language (and a dick pic). As the ride goes on and the conversation with Penn gets more deeply personal while she’s simultaneously dealing with this other man via text on her phone, you can see her luminous veneer chip away a bit.

“Daddio” is the first film helmed by writer/director Christy Hall, and she gets everything right. With the help of cinematographer Phedon Papamichael, we get plenty of closeups of the stars plus a few exteriors as the cab winds its way to its destination. Yet it doesn’t feel static or claustrophobic — it feels like we’re in the taxi, too, listening covertly — and the interior is very smartly lit so we can always see the characters’ eyes, which offer great insight into who they truly are.

Johnson’s performance is pitch-perfect as she balances interactions between the man she’s texting with and the cabbie in the front seat, becoming more nuanced as the story develops. Meanwhile, Penn projects the world-weariness of a cabbie who’s been on the job for twenty years — and it shows in his craggy face. Hall has him curse up a storm (as if to prove the man’s New York City bona fides) as he talks about his life and sizes up this woman in his back seat. Major kudos to Johnson for not letting herself get run over by Penn’s energy and intensity.

Hall originally intended “Daddio” to be performed on stage, but then morphed the script into a screenplay which sat around for a couple more years until Daisy Ridley showed interest. But that never blossomed into anything, so Hall had to keep shopping it around Hollywood until it reached Johnson, who agreed to both produce and star in it. I’m glad she did because the finished product is a terrific character study with two top-tier performances

I give “Daddio” an 8.5 out of 10. Opens tomorrow in theaters.