‘The Friend’ gives Naomi Watts a terrific co-star. Yes, he’s a Great Dane.

Pity the poor actor who has to co-star opposite a 150-pound harlequin Great Dane. This is what happens to Naomi Watts in “The Friend,” except in this case no pity is required. She gives one of her best performances ever. The Great Dane is no slouch, either.

I should state up front that this is not a typical rampaging-dogs-and-their-frazzled-owners funfest. Loosely derived from Sigrid Nunez’s National Book Award-winning novel, and co-written and co-directed by Scott McGehee and David Siegel, it’s about coming to terms with grief. The comedic moments, and there are many, are laced with melancholy.

Iris (Watts) is a college writing teacher in New York who has been struggling to finish a novel. Her closest friend and mentor, Walter (Bill Murray), has taken his own life, and the suddenness of his death has left her bereft. It was Walter’s wish that Iris, who is single and lives alone, inherit Apollo, his 6-year-old Great Dane.

At first she flatly refuses. Her rent-controlled Greenwich Village studio apartment has a strict no-pets policy. And besides, she’s a cat person. But she grudgingly takes in Apollo, avoiding the nosy building superintendent (Felix Solis) until she can unload Apollo elsewhere.

You can see where this is going, although the route has many emotional circumlocutions. Iris’ despair over losing Walter, whom we mostly observe in flashbacks, is a pastiche of rage, resentment, and sorrow. A renowned novelist and notorious, thrice-married cad, Walter was also a world-class charmer. But his connection to Iris, once his student, was essentially inspirational, not romantic. This is what hurts her the most – she has lost a soulmate.

The omnipresence of Apollo in her life reinforces her sense of loss, especially since it’s clear that Apollo is also grieving. A worn T-shirt of Walter’s is his constant comfort. I’m always amazed when so-called experts claim that only humans can comprehend death. As a rebuttal, this movie should be offered up as Exhibit A.

I don’t know if one can rightly call Apollo’s performance a performance. But whatever it is, it’s heartfelt. (The dog’s real-life name is Bing, and thanks must go to his trainer, Bill Berloni, and owner, Bev Klingensmith.)

The filmmakers are certainly cognizant of the comic disparity between Iris and Apollo. When her friendly neighbor Marjorie (Ann Dowd) first walks in on them, she says to Iris, “There’s a pony on your bed. A very sad pony.” In fact, for a time, Iris sleeps on the floor because Apollo has claimed the bed. But the humor in their situation never devolves into slapstick, even when Apollo, left on his own, tears up the apartment.

In some ways, “The Friend” is like a serious take on the terrific 1989 comedy “Turner & Hooch,” in which Tom Hanks plays a fastidious police officer who inherits a slobbery French mastiff from a murdered friend. The two films mostly couldn’t be more different, but what they share is an all-out embrace of the (eventual) bond between human beings and the dogs to whom they are devoted.

Given the pitfalls of gush and treacle in this type of material, “The Friend” is no small achievement. Is it impertinent to say that Watts has never had a better partner in the movies? The levels of emotion she brings to the role clearly have much to do with her co-star.

If I have focused primarily on Iris and Apollo here, it’s because those are the sequences that stayed with me. As for the film’s other aspects, despite a slew of fine additional supporting performances by the likes of Carla Gugino and Sarah Pidgeon, it dabbles in psychobabble. Iris has a grief session with a psychiatrist that spells out what doesn’t need to be spelled out. The depictions of the New York literati scene, with its backbiting and wary camaraderie, are effective but all too brief. Murray is well cast as Walter, but his scenes are few. And the film seems to end at least three different times.

For dog lovers, and for people who love intelligent movies about dog lovers, none of these faults may matter much. I’m in that camp.

Peter Rainer is the Monitor’s film critic. “The Friend” is rated R for language, including a sexual reference.