True confessions time.

Netflix has decided “hot for teacher” movies fit my algorithm. I don’t know why, as most of the movies of this warped little corner of thrillerdom that I review aren’t on Netflix, although many turn up there eventually.

And they’re pitched to me by film distributors, not films that I hunt down by subject matter.

But somehow, Netflix has ID’d movies about students getting romantically/sexually involved with a teacher as something they expect me to like. Ick.

Granted, they are popular, as I searched that phrase on this blog and several movies a year wear that genre label (with apologies to Van Halen, copyright pending). And I know for a fact that reviews of such movies are real reader magnets.

So yeah, I’m a little embarrassed. Maybe you should be, too.

“Black Island,” titled “Schwarze Insel” in its original German, is an erotic mystery thriller set on an unnamed Frisian Island. It’s a somewhat suspenseful tale of an old grudge and revenge that’s best served seaside.

I say “somewhat suspenseful,” because co-writers Miguel Alexandre (who also directed) and Lisa Carline Hofer give away parts of the game too early, and make another misstep or two on their way to a satisfying finale. Somebody should remake it and make the necessary adjustments as they do.

A brief prologue shows us a tragedy that happened on this island. And the funeral connected to that tragedy has an unhappy ending as well. But “tragedy” implies “accident.” And these “accidents” were planned. We see who carried those plans out.

Teenaged Jonas (Philip Froissant) is newly-orphaned. His friends are his only real comfort, especially Nina (Mercedes Müller) who might be a little sweet on him.

She’s depressed about the idea of him moving away to live with distant relations. But his estranged grandfather (Hanns Zischler), a retired schoolteacher, invites him to stay on and live with him.

A year later, a new German language and lit teacher takes over, midterm. Jonas, Nina and their friends are taken with Rilke buff Helena Jung (Alice Dwyer of “The Invisibles”). She even invites them over to put together her new IKEA furniture and install a little flooring.

She gives them beer. She tells them to call her “Helena.” Jonas seems to get her special attention. And that puts Nina, who doesn’t want the competition, on her guard.

Helena coyly defuses that with her “Are you guys an item?” queries (dubbed, or in German with English subtitles). But sooner rather than later Jonas takes the bait, and lets Helena’s “We’re both adults” rationalization ease his conscience.

Poor Nina. But she’s a smart kid, and a sly one. Nina, we suspect, is going to figure some things out.

“Black Island” finds charm in the way Nina courts Jonas, and sad resignation in the way he betrays her.

And in Dwyer, it has a first rate villainess, a schemer with just enough “crazy” behind her eyes to make this character work. She is subtle enough to never let us see the Full Glenn Close, but never leaves any doubt that she’s a woman with a mission and a grudge. Dwyer and Helena take over the film, which takes on her “Talented Mr. Ripley” point of view.

Whatever she’s done and she’s going to do, we’re privy to it, and to Helena’s efforts to tidy up in the aftermath.

I have to say the film’s set-up is more interesting than the resolution, which is seriously straightforward.

But the violence isn’t “Hollywood,” it’s human. And the remote, windswept setting has its chilling pleasures as well.

That makes this mixed bag of a movie a little more than “exploitation,” a little less than a fully functional thriller.

And if your algorithm tags you as a “hot for teacher” genre completist, it’s worth a look.

Rating: TV-MA, violence, sex, some nudity, teen drinking

Cast: Alice Dwyer, Philip Froissant, Mercedes Müller Hanns Zischler

Credits: Directed by Miguel Alexandre, scripted by Miguel Alexandre, Lisa Carline Hofer. A Netflix release.

Running time: 1:45