Two things we’ve been conditioned to expect from the “slow-burn thriller” is that it A) IGNITE at some point, and B) have a certain logic to it.

The Spanish drama “The Occupant” doesn’t want to play by those rules. It simmers towards a boil that takes an awful long time coming. And the motives in the beginning and bizarre leaps the plot takes make you wonder when we are ever going to get “there,” and when we abruptly arrive, how we got “here.”

It’s a genre piece, another story of what the newly-employed middle aged professional man does, in secret, when his family thinks he’s off restarting his career, working at a new job or at least taking classes.

Javier Gutiérrez (“Assassin’s Creed”) stars as a Javier Muñoz, a 50ish family man who has had a successful career in advertising, emphasis on “had.” He’s been out of work for a year, has a hard time finessing the reasons for that in job interviews.

And in the capture-the-youth-market world he’s made his mark in, he cannot hide the grey hair or hidebound nature of his portfolio.

If we think the final humiliation will be the offer of job that turns out to be three month “unpaid” internship, we aren’t reckoning on how life is shrinking back home.

Wife Marga (Ruth Díaz of “The Skin of the Wolf”) has to take a job in retail. She suggests they sell his BMW. He wants to reassure his teen son that he can keep going to the uniformed private school he attends. The kid is resigned to giving that up. They can move to an old family apartment in a more modest building, and give up the posh place with its stunning view of the city.

And then there’s the maid, who weeps at being let go, then turns furious. No night school class/motivational seminar is going to make all this go away.

But he still has the keys to their old place, still has access to the parking garage. Damned if Javier doesn’t start ducking into the old place — raiding the fridge, using the toilet, and hacking into the family computer.

The more he does this, the deeper into messing with their lives he gets. Poisoning a neighbor’s dog who barks every time he shows up tells us how far gone this guy is.

Does he get his jollies, discovering new “occupant” Tomás (Mario Casas of “The 33”) is a recovering alcoholic, that he had a bad car wreck, that he is probably on a short leash with his wife (Bruna Cusí) and little girl?

That’s a big question left unanswered in this Alex and David Pastor (“Carriers”) film. What is Javier’s game, and what — aside from the flimsy obvious motivation — is driving him?

Without having a handle on that, we’re disinterested observers in Javier’s schemes, his manipulations and those who might get wise to what’s going on and manipulate him.

You can appreciate how this or that piece of foreshadowing plays out, how he ingratiates himself into these new lives and how he avoids this trap or sets that one.

But the script and characterization never let us invest in this character, or any other. Maybe we fear for this or that hapless victim. Maybe we root for “The Occupant” to finish whatever his sinister scheme is.

But when the slow burn is this slow coming to a boil, it’s a lot easier to just shrug and move on to a thriller that makes more sense.

MPAA Rating: TV-MA, violence, sexual situations, profanity

Cast: Javier Gutiérrez, Mario Casas, Bruna Cusí, Ruth Díaz

Credits: Written and directed by David Pastor, Àlex Pastor. A Netflix original.

Running time: 1:43