A lot of movies keep their secrets well enough that they make you wonder, “What the hell is this thing about?” It’s not often that a film frustrates even veteran mass consumers of movies like me with that feeling over an hour into the viewing.

“Ultrasound” is a maddening mystery of multiple but mysteriously interconnected timelines and sets of characters, a movie the revels in its confusion. When it finally starts to reveal its point, you don’t feel rewarded for figuring it all out — because you haven’t. You just feel relieved in an “OK, sure, now I get it” and “Oh, I’m not losing it after all” sense.

It begins with a car accident that wasn’t an “accident.” We’ve seen spiked boobytrap that blew his tires in the rain, and maybe we’re not surprised when the couple who take in the driver, Glen (Vincent Kartheiser of “Mad Men”) seem…off.

Art (Bob Stephenson) is too friendly, too chatty and much older. Meeting his wife (Chelsea Lopez) is jarring, as she seems fragile and trapped. He’s too quick to share his “manic depression.” But she’s over-shared that first. That’s before she lets on that she “married my high school teacher.”

“Pretty f—-d up, huh?”

Glen is put on his guard and on his heels, wrong-footed long before the suggestion that he spend the night with the wife. His outraged protests segue to Glen and Cyndi, deep in discussion, on her marital bed.

There are these jarring jump-cuts, a flash of just a few frames of film jolting Glen to another reality, another take on the situation. There’s a ringing in his ears.

And…SCENE.

Katie (Rainey Qualley of “Ocean’s Eight”) is doing laps in a public pool, fending off the rude attentions of a creeper. She’s pregnant. Or is she? There’s an assignation with the mysterious Alex (Chris Gartin) she’s late for.

Is Cyndi pregnant, too? How does Glen end up in a wheelchair, and what do the folks in lab coats (Breeda Wool, Tunde Adebimpe) have to do with all this?

Cryptic scenes follow other cryptic scenes, conversations seem to reveal much, or nothing of importance. Connections between characters are so flimsy that you wonder if there’s been a mistake in the editing or the processing of first-time feature director Rob Schoeder’s film of Conor Stechschulte’s obscurant screenplay.

We know the title. We hear the ringing tones, and get those David Lynch/John Carpenter subliminal flashes that hint at time, memory or reality being distorted, which sets us up for most anything.

And then the fog clears and a much more recognizable and conventional thriller unfolds.

The marvel here is how long “Ultrasound” keeps us off-balance and lost, how much the filmmakers are willing to test the viewer’s patience and the risks involved in making this sort of movie mystery in the age of streaming. It’s one thing to be trapped in a theater, ticket purchased and thus forced to accept an unfairly challenging movie on its own terms. It’s quite another when the viewer has the option of shouting “EFF this” at whatever home screen they’re experiencing this on and moving on.

“Ultrasound” challenges us to go with our instincts and first impressions no matter what we learn about characters later on, only to upend those impressions on occasion. It puzzles and annoys and maybe even infuriates.

When even the “Ahhh, so that’s what’s going on” isn’t the easy, unearned and spoon-fed reward it seems to be, you know you’ve been tested by a movie that isn’t giving you enough information for that to be a fair game.

Rating: unrated, violence, profanity

Cast: Vincent Kartheiser, Chelsea Lopez, Breeda Wool, Rainey Qualley, Tunde Adebimpe and Bob Stephenson

Credits: Directed by Rob Schroeder, scripted by Conor Stechschulte. A Magnolia/Magnet release.

Running time: 1:43