Veronica, “Ronnie” to her friends, sees dead people.

But that’s OK. Everybody does. Ever since “The Event.”

And in “a world where the dead walk among the living,” there are rules. “They can’t alter their imagery…They can’t affect our natural world.”

That’s what the experts tell us. But why is there “a panic room in every house” if the dead can’t hurt us? If they can’t “affect our natural world,” why does a ghost, a “remnant,” keep showing up in Veronica’s shower, writing “RUN” on her bathroom mirror?

Aside from the fact Veronica is played by Bella Thorne, I mean?

“I Still See You” is a middling mystery thriller in which the supernatural is explained and over-explained by long bursts of exposition, “rules” and scientific gobbledygoop delivered by the smartest science teacher in Jewel City, Illinois (Dermot Mulroney), as well as a science nerd who’s been paying attention in class, and the obsessive “James Dean type,” the brooding and quiet Kirk Lane (Richard Harmon).

Guess which one Ronnie believes?

Ten years after “The Event,” life goes on in much of the country. “Ground Zero” was Chicago, now a “No Go Zone.” But in Jewel City, people like Veronica stare at dead people — like her dad, sitting, sipping ghostly coffee and reading the newspaper at breakfast every day — then vanishing in a puff of ashy smoke.

It’s a morbid, bittersweet existence, not helped when a long-dead woman pops up in science class, or an old man goes through the motions of leaf-blowing his lawn even though its covered in snow. At first, they thought it was just people killed in “The Event.” Now, Veronica and others are becoming “truthers,” like Kirk. They don’t know what to buy into. The “remnants” seem to be growing in number.

Ronnie is being stalked by this underwear model with murder in his eyes every day in the shower gets her attention. Who is he, why is he in her bathroom and does he mean her harm?

The overriding explanation for all this is a Hiroshima/Nagasaki comparison. Whatever happened in Chicago turned people into shadows of themselves, some trapped in a “loop” capturing the moment of their death, others intentionally drawn to some place and time very special to them.

It’s a bit like religious teaching, isn’t it? Damned to hell, or somehow “sentenced” to heaven — a pleasant memory.

But Ronnie starts to see her stalker everywhere. An effective moment — Thorne’s Veronica lunging through the gym in the middle of a basketball game, touching people to see if they’re real. She brings the game to a dead silent halt.

There are ice skating reveries and falling-through-the-ice nightmares, a murdered young woman whose birthday matches Ronnie’s and an imaginary clock ticking towards Ronnie’s doom. Apparently.

Thorne is a real “gather ye rosebuds” movie (and music and TV and what have you) star, not the most selective in what she does, just getting while the getting’s good. She works constantly and not every film she takes on has the edge of “Assassination Nation” or camp of “You Get Me” (stalker girl) or the action beats to deliver real thrills of “Big Sky.”

She tries to bring a little flippancy to her line readings, going for throw-away laughs when she bats her eyes at the science nerd “obsessed with me since seventh grade” for help.

“Still got it.”

Her “Midnight Sun” director Scott Speer doesn’t do much with the potential romance here, letting the ripple effects that we see when somebody gently touches a ghostly image, and the ashes caught in the SFX wind when you storm through a “rem” (remnant) do the heavy lifting. Pretty, as are the underwater sequences.

While “I Still See You” has a nice wintry gloom, some creepy settings, it never manages more than a few minor thrills and a couple of chills.

Nobody registers fright, which I guess is to be expected if ghosts have become as commonplace as Kardashians — just something we live with.

But if Thorne wants to become the new “Scream Queen” (Who’s to say?), she’s going to have to give us more than this — anxiety, terror, panic, URGENCY. It’s not part of her repertoire yet, and considering how much we STILL see her — online, in movie after movie, music videos of her own creation and TV shows — she should have picked that skill set up somewhere along the way.

She may be the hardest working woman in show business. But it’s not just working a lot or working hard that counts. Being picky wouldn’t kill her.

MPAA Rating: PG-13 for some violence, terror, partial nudity, and thematic material

Cast: Bella Thorne, Dermot Mulroney, Sara Thompson, Richard Harmon

Credits:Directed by Scott Speer, script by Jason Fuchs, based on the novel by Daniel Waters. A Lionsgate release.

Running time: 1:44