A good time travel movie doesn’t have to cost a lot. The Spanish “Time Crimes” the American indie jewel “Primer” prove that.

All it needs in order to succeed are engaging characters, a ticking-clock plot and a thought exercise that we can wrestle with as the picture unfolds, and in the days after seeing it.  Good films of the genre, from “Back to the Future” on down the line, invite us to work out the chronology, the “logic” — not so much of the time-travel device, the way it happens, but in how characters cope with the the timeline, and avoid (or succeed) running into versions of themselves.

“Time Trap” (“Timetrap” it appears in the film’s actual credits) makes a go at the first prerequisite, ignores the second and manages to make a complete hash out of the third.

No “mulling it over” when it’s done. It’s too damned dumb for that.

The Mark Dennis/Ben Foster film (“Strings”) weaves in a little “Fountain of Youth” here, some of H.G. Welles’ “The Time Machine” there, stuffing its protagonists in a cave where things go wrong, people get hurt and die and it takes them a very long time to figure out that outside of the cave, time is skipping by in a blur.

A Texas academic archaelogist (Andrew Wilson) has been hunting for people who disappeared in the high desert decades and decades ago. We meet him as he’s gotten his best clue, and hustles back to his house for gear to duck into a cave he needs to check out.

He orders his grad assistants (Brianne Howey, Reiley McClendon) to stay behind. He and his dog will look into this cave. They have a notion it’s the mythic Fountain of Youth he’s looking for. Hitching their academic wagons to a flake? Maybe.

Naturally, Jackie (McClendon) and Taylor (Howey) resolve to go after him. And just for efficiency’s sake, they hit up another student, Cara (Cassidy Gifford, yeah she has famous parents) with access to her dad’s SUV.

She brings along camcorder-crazed little sister Veeves (Olivia Draguicevich) who in turn,insists they drag along an even younger friend of hers, a kid named Wallace but who prefers “Furby” (Max Wright).

They track down the professor’s van, can’t raise him on the radio, and decide to follow him underground. Things start to go wrong the moment they do.

The clues the movie gives us about this cave and what’s in there are a creepy noises, suggestions that others came through here long along, a glimpsed cowboy here, primitive not-quite-Morlocks (from Welles’ “The Time Machine”) there.

The story’s great leap forward in exposition is one of the lamest I’ve ever seen — “Timetrap” is reliant on “found footage” of how this character read that “journal” someone left behind, or footage of how a character came to a grisly end.

A faint attempt is made at telling the story with parallel structure, letting us see Dr. Hooper’s poking around cutting back to the students’ search for him. That proved too complicated and was abandoned.

Whole threads of the story go out the window, too.

And while the third act has a couple of modestly exciting cliffhangers (hanging from a cliff, or a ladder) and some very good effects, the whole affair is more of a head-scratcher than anything you’d recommend.

The moments of pathos are kept short and never referred back to, in spite of the presence of a body from one of their number still within reach. Short mourning period when you’re trapped far below, I guess.

The cast is young and attractive, but the characters are poorly developed. Some semblance of giving every searcher a special skill — the best rock climber, the one person who knows how to drive a stickshift Land Rover, the photographer — is instantly dropped.

And the dialogue is duller than most any conversation you’d overhear at Starbucks.

“Wait, it could be a BOOBY trap!”

“Relax, this isn’t ‘The Goonies.'”

“What’s a ‘Goonie?'”

Nobody wants to speculate, nobody “explains,” nothing important, anyway. Not unless it’s on video.

It’s not the worst time travel tale ever, but it does earn the most dismissive assessement you can give a movie in this genre.

It’s not worth your time.

MPAA Rating: unrated, violence

Cast: Olivia Draguicevich, Andrew Wilson, Cassidy Gifford, Brianne Howey, Reiley McClendon and Max Wright

Credits: Directed by Mark Dennis, Ben Foster, script by Mark Dennis.  A Paladin/Netflix release.

Running time: 1:28