“Missionary” is a lean, slickly sordid indie thriller about a Mormon missionary who goes bad. Really bad.

Take away the not-so-saintly Latter Day Saint element and it would only occasionally rise to generic, a simple love triangle turned deadly. But add a little sin and a hint of insanity, suggestions of church complicity in the unfolding tragedy and you’re bound to punch somebody’s hot buttons.

You see them in pairs, young men in white button-down shirts and ties, riding Schwinns and spreading the word about The Book of Mormon. They’re men on a mission, a rite of passage among the Latter Day Saints, going door to door in America and all over the world on self-financed outreach missions, recruiting for the church.

In central Florida, Elder Whitehall (Jordan Woods-Robinson, convincingly earnest) shows the ropes to Elder Brock (Mitch Ryan, charming yet chilling) drilling him on which scripture to quote when counter-arguments come up among the not-yet-converted. They track their progress on a board — “Finding” some potential members, “Teaching” others whom they’ve sensed an interest, “Baptizing” the converted.

They have a lot of rules. They must stick together, travel in pairs to avoid temptation. They will live a strict abstinent life on the mission. And, apparently, they’re not allowed to goof off and play sports.

That’s the one that trips up Elder Brock. The shapely Katherine (Dawn Oliveri, earthy and beguiling) is trying to teach her boy to throw a football. Elder Brock can help. Fine. That gets the missionaries in the door, as she feels a little quid pro quo is in order. She lets them pray with her and her son.

But, the newly-separated Katherine notices what a hunk this missionary is. And when chance throws them together alone, she makes her move.

“Missionary” turns sexual before you can say “position,” and before we know it the script has abruptly launched a Cougar and Christian dalliance that turns ugly the moment the not-quite-ex husband (Kip Pardue) re-enters the picture.

Elder Kevin Brock may spout off about creating a baptized Mormon family, headed by him and including Katherine and her kid Kesley (Connor Christie). But plainly, all that “pressure” he spilled his guts about, barely prompted, has gotten to him. He snaps in a heartbeat. And he goes from proselytizer to stalker in another heartbeat.

That’s a major shortcoming of “Missionary,” the leaps of logic and plot devices that clumsily slot together to move us from our first sanitized view of Brock to capable-of-anything man-scorned. A supposedly guarded missionary spilling his guts to a non-believer/stranger rings hollow, and it’s all downhill from there.

Katherine may be the best-looking woman ever employed in a junkyard, pulling old parts for DIY car repair.

Kevin’s racial attitudes are quoted as church dogma, his voracious appetite for forbidden sex is more uncorked than developed believably.

Where the recent church-sponsored documentary “Meet the Mormons” sugar-coated the present-day Latter Days, and was widely criticized for painting over some of the more unpleasant positions of recent church history, “Missionary” airs them — right up to the edge of Mormon bashing. The racism Kevin blurts out, supposedly now out-of-date within church teachings, the suggestion that he’s been treated the way the Catholic Church treated problematic clergy, lacks the subtlety that would have made those attitudes feel less like inadequate research instead of agenda-driven screenwriting.

That missionary commitment has been the setting for a pretty good crisis-of-faith drama (“God’s Army”) and an amusing crisis-of-sexuality comedy (“Latter Days”). So there’s no reason the missionary-recruiter turned stalker idea couldn’t work. But this one doesn’t.

MPAA Rating: R for violence, sexuality and language

Cast: Dawn Oliveri, Mitch Ryan, Kip Pardue, Connor Christie, J. LaRose

Credits: Directed by Anthony DiBlasi, written by Bruce Wood, Scott Poiley . A Freestyle release.

Running time: 1:30