Ansel Elgort makes subtle work of Every Actor’s Dream, the chance to play two characters in the same movie, in “Jonathan.”

It’s a downbeat and curious sci-fi drama about a young man whose identical twin wasn’t so much in the womb with him as in his actual body.

Jonathan and “Jon” are trapped, but science and reason — in the person of Dr. Mina (Patricia Clarkson) — have found solutions.

They will live separate lives in the same tastefully Spartan apartment. One has dreams of a career, and will go to work and keep, rigidly, to a daylight-only schedule. The other will be the night owl/barfly, “having fun” until the wee hours.

They keep a shared video diary to keep track of who did what, and with whom, the day or night before. Neighbors, colleagues, women who might be interested are documented each late afternoon for one, each late night by the other.

“I ran into Sarah in the lobby and helped her with her groceries. So in case you see her, that’s why she loves you so much.”

Daytime Jonathan, called “Jay” by his sibling, is organized, studying French, a draftsman and rising star in architecture. Only he can’t put in the hours to make that big leap.

Slacker night owl “Jon” doesn’t do his share of the chores, doesn’t get in early enough for them to be rested and doesn’t share everything.

“Having a girlfriend’s against the rules,” and he knows it. But did he break it off as he said he would?

Enter the private detective. Organized Jonathan isn’t able to investigate on his own after hours, so enter Ross Craine (Matt Bomer). He’s puzzled about how one guy can be “both the client and the mark…a somnambulist or something?”

But he’s the one who figures out Jonathan’s being lied to. There’s a girlfriend, the bartender Elena (Suki Waterhouse). That’s upsetting to daytime Jay, because, well just because.

“Everybody has a routine.”

“Well, you run yours like a German train.”

First-time director/co-writer Bill Oliver takes this premise about as far as it will go, and in directions that we see coming the moment we meet Elena. A woman will come between them, seeing attractive traits in each despite their disparate personalities.

The melodrama that ensues only approaches something trippy and sci-fi in nature late in the third act. There’s no “Being John Malkovich” wit and whimsy to this, no “Dead Ringers” menace to raise the stakes and heighten the tension.

It’s almost entirely from straight-arrow Jonathan’s point of view, a mistake that dulls down the proceedings. The conflict feels low-stakes, even when life or death are involved.

“Jonathan” plays like an intellectual puzzle that isn’t challenging enough, an acting exercise that has everything but emotional connection and a tour de force robbed of its force by just lying there, inert when it should be picking up steam, cold when the characters and scenario should be heating up.

MPAA Rating: unrated

Cast: Ansel Elgort, Patricia Clarkson, Suki Waterhouse, Matt Bomer

Credits:Directed by Bill Oliver, script by Gregory Davis, Peter Nickowitz and Bill Oliver. A Well Go USA release.

Running time: 1:35