Zach loved Beth — past tense. But his girlfriend put in her earbuds, trekked off up into the hills, and…something happened.

Because we meet Zach (Dane DeHaan) after her funeral. He’s in shock. His parents (Cheryl Hines, Paul Reiser) are ready to move on to “Life After Beth.” They talk up vacation plans. But even though Beth’s folks (John C. Reilly, Molly Shannon) may be barely maintaining a brave face, they make time to comfort him. Heck, Morty (Reilly) even shares one of Beth’s joints with him as they play chess into the wee hours, fretting over the last words each said to her before that fateful hike.

That doesn’t help. Zach grows more morose and more obsessed. They give him a woolen scarf, which he wears in the summer.

“It’s my dead girlfriend’s scarf. She’s DEAD.”

Jeff Baena’s “Life After Beth” has a variety of fascinating directions it can head off in at this point. The college boy’s unhealthy fixation, the adults’ insistence on moving on, the girls’ desire for escape.

And when Beth reappears, there are still plenty of options as to where this could go.

“What kind of grift is this?” the kid demands of his dead-now-alive girlfriend’s father. A grift would be odd and kind of funny, maybe an insurance scam or something. Maybe they’re trying to free their daughter from this lunatic boy she’s in love with. But no.

“It’s a…resurrection!”

“Life After Beth” — the title is a pun — is about Zach’s comical confusion about how to react to this heart-wrenching loss that no longer counts as a loss. All those things he never got to tell her?

“Go! Say everything you meant to say to her!”

But Beth? She’s DIFFERENT. She has no memory of being dead, and since she’s played by Aubrey Plaza, that means a lot of eye-rolling.

She’s volatile, violent and sexually insatiable. Musically, she can only tolerate smooth jazz. And her parents are acting just as strange. Her mom can’t stop taking pictures of her, urging them to go off and, you know, be alone. Her dad wants to keep her indoors. Especially during daylight hours.

“Discretion, Zach. Discretion.”

Zach hints that he has a clue. He must have seen “Twilight” or “The Walking Dead.” What’s clever here is how he ignores what he’s figuring out and what the adults may not be telling him. Beth, for a while at least, is the most fun she’s ever been and they can’t get enough of each other. He’s not questioning that.

DeHaan doesn’t get across Zach’s grief in the early scenes or his desperate denial in the later ones. He simply mentions these feelings.

Plaza (“Parks and Recreation”) on the other hand, is all-in for this romp, veering between dopey and demented.

“Life After Beth” attracted a good cast — Garry Marshall is a grandparent, Anna Kendrick shows up as “a girl I knew from childhood” — and this dark comedy has a lot of promise for about half its length. Then, unfortunately, it settles into the mundane genre picture that it seems doomed to be.

Whether it was his choice or one dictated by production financing, “Life After Beth” contents itself with taking that road well traveled to a genre of film that has been shot, bludgeoned and beaten to death.

MPAA Rating: R for pervasive language, some horror violence, sexual content, nudity and brief drug use

Cast: Dane DeHaan, Aubrey Plaza, Anna Kendrick, John C. Reilly, Cheryl Hines, Paul Reisner, Molly Shannon

Credits: Written and directed by Jeff Baena. An A24 release.

Running time: 1:29