In “Reptile,” the only thing that matters isBenicio Del Toro.

这部电影需要侦探小说的形式,但如果你focus only on that, you’re bound to find the movie a bit slow. Pay attention, instead, to Del Toro, who plays the detective. If you’re watching “Reptile” in the right way, you’ll find yourself becoming even more interested in how the case is impacting the detective’s life.

A movie can only accomplish that kind of shift in a viewer’s interest — from something external and dramatic to something internal and personal — if the actor we’re looking at is actuallyworthlooking at. It helps if the actor is also given interesting things to do, but mainly it’s about the complexities of thought, soul and emotion coming through an actor’s face.

Here Del Toro looks very cool and yet often sounds surprisingly uncool. He is mostly gentle and polite, while conveying that it would probably be a mistake to make him angry. His heavy-lidded eyes make him look as if he’s going through life half asleep, and yet he seems to notice everything. And while he never makes a grand display of his feelings, he leaves you in no doubt that his emotions run deep.

In a sense, Del Toro has been like that in every movie he’s ever made. But in “Reptile,” which he co-wrote, there’s just more of him — and as it turns out, more is fine.

Early in the movie, the wife of a prominent real estate agent (Justin Timberlake) is murdered, and Nichols (Del Toro), a small-town detective, is given the case. For him it’s just another assignment, not his mission in life. But gradually, the case starts to impact him personally.

The casting is good, in that it seems to have been done with the idea of showcasing Del Toro and his character. For example, Alicia Silverstone plays his wife. That’s a rather unusual pairing because they don’t seem like the typical movie couple, but rather like two people who’d actually be married in real life. You could see why a shrewd, loquacious woman would be attracted to this benign, granite-like guy, and vice versa.

In the same way, every other actor in the movie — from Timberlake, to Eric Bogosian as Nichols’ boss, to Domenick Lombardozzi as his colleague — seems to have been cast as an irresistible force to be thrown against Del Toro’s immovable object.

In his feature director debut, Grant Singer (previously a music video director who’s worked with artists fromSam SmithtoSkrillex) adopts a measured pace that lends the movie a somber, mysterious aura. But he breaks that up with smart, psychologically insightful cutting. In one scene, we hear Nichols talking to a psychiatrist, while the movie shows us the installation of a new kitchen sink in Nichols’ house that turns on if you just wave your hand near it. He saw a sink in the victim’s house and wanted one just like it.

It’s possible that the director could have picked up the pace a little, but “Reptile” (the title refers to a snake skin found in the victim’s house) is so good I wouldn’t presume to mess with it. At the very least, Singer deserves credit for shedding his own video-directing skin and for wholeheartedly throwing his film to Del Toro.

再保险ach Mick LaSalle: mlasalle@sfchronicle.com