The questions pop to mind early and somewhat often in the new thriller “Echo Valley.”

Wait, how did that tiny young woman lift…Her 60something mother chose what to dump a body in a lake…So did the ex-husband take up with a much younger woman before his wife discovered she was gay?

Some mysteries are solved and some left hanging in this engrossing will-they-get-away-with-it mystery from the director of “Beast” and the writer of “Mare of Easttown.” But the one we’re left to ponder entirely to ourselves is “How could anmother capable of the sort of unconditional love we see here raise such a monster?”

Oscar winner Julianne Moore plays the mother, Kate, a widow still grieving the death of her wife, still living on the Chester County, Pennsylvania horse farm she kept in the divorce (Kyle MacLachlan plays the ex), still waiting to hear from her irresponsible, self-absorbed addict-daughter, played by “It” girl Sydney Sweeney of “Euphoria” and “Anyone But You.”

Things are bad enough enough, what with Kate canceling riding lessons in her grief, the farm running in the red and the ex fed up with writing checks. Then the headstrong addict Claire shows up, with her druggy beau (Edmund Donovan), empty promises — “I’m CLEAN, Mom! I’m good.” — and a need for cash.

There’s a dealer (Domhnall Gleeson) with news that Claire “betrayed my trust. Your junky daughter has two choices. Give it back or she can pay me my money.”

As the opening scene of the film is a body coming to the surface of a nearby lake, the questions begin. Who is it? Who sank it? And will she/they/etc. get away with it?

It’s all handled reasonably well, with just enough twists to hold the interest and just enough attention to the logic of it all for Brand Ingelsby’s script to make sense — more or less.

Moore is wholly believable as a woman gutted by loss, trapped by her devotion to a kid who’s just no damned good. Sweeney makes Claire recognizably lost, following her impulses, but cynically sure of one thing — her mother’s willingness to do anything to help her. It’s one of her best performances.

Gleason makes a sharp, sinister villain. And Fiona Shaw sparkles as that ride-or-die lesbian pal a gal needs to lean on in a pinch.

“Echo Valley” isn’t great, but it isn’t bad. And the fact that it’s on Apple TV means you don’t have to keep your questions to yourself. Shout at the screen as much as you like. I know I did.

Rating: R, violence, drug abuse, profanity

Cast: Julianne Moore, Sydney Sweeney, Fiona Shaw and Domhnall Gleason.

Credits: Directed by Michael Pearce, scripted by Brad Ingelsby. An Apple TV+ release.

Running time: 1:44