The directing debut of writer-actor Mike White, "Year of the Dog" is not so much a departure from his auspicious earlier screenplays as it is an extension on many of the themes running through his work. A dialogue craftsman who can mix bitingly droll and delicious comedy with cathartic, at time heartbreaking, drama, White seems especially fascinated in the personal lives of people struggling to find happiness and their rightful place in the world. His latest effort, like 2000's "Chuck & Buck," 2002's "The Good Girl," and to a lesser extent 2003's broader "School of Rock," is such a tale, as affectionate and gentle as it is sometimes downbeat and touching.

In the juicy film role that has eluded her since leaving "Saturday Night Live" several years ago, Molly Shannon (2006's "Marie Antoinette") gives a multifaceted Oscar-caliber performance of insight and subtlety. She plays Peggy Spade, a 40-year-old singleton who has always found herself to share more compatible bonds with animals than people. She has an office job by day, a coworker friend in the marriage-obsessed Layla (Regina King), and a pleasant relationship with her squeaky-clean suburbanite brother Pier (Tom McCarthy) and sister-in-law Bret (Laura Dern), but Peggy's real joy comes from her beloved dog Pencil. They cuddle while watching TV, eat dinner together, share a bed at night, and are all around best buddies. When Pencil tragically dies after staying outside all night and ingesting a toxic substance, Peggy's worst nightmare is realized—facing the death of her only child.

A serenade to animal lovers and a soft-hearted ode to anyone who has ever felt different, "Year of the Dog" exclusively remains by Peggy's side as she navigates a life without Pencil and begins to dabble in everything from veganism to pet adoption to animal activism, her devout passions eventually running the risk of getting out of control. The film is sporadically a little frothy for its own good, but it is also this simplicity that makes it endearing. The characterizations of not only Peggy, but also the supporting characters, are exactingly realized, the writing marvelously balances shifting light and dark tones, and the story goes in provocative directions that aren't easily predicted.

There are big laughs to be had in writer-director Mike White's sharp human observations—watch the way reserved Peggy uncomfortably responds to next-door neighbor Al (John C. Reilly) when they go out on a date and he asks her if she's ever been married—as well as in his skewering of stereotypes. Pier and Bret, for example, have a soccer-mom mentality—when Peggy gives their daughter "Babe" on DVD as a present, Bret pensively comments that she's heard the G-rated film has "quite a bit of dramatic content"—but they are also loving people who respect the lonely Peggy without looking down on her. The same goes for Layla, who enjoys spending time with her even if she usually points their conversations toward matters of the opposite sex. As for Peggy's relationship with Newt (Peter Sarsgaard), a fellow animal lover and veterinarian assistant, a possibility for a romance between them is cut short when he declares his practicing celibacy. From there, she must reassess what he means to her and what she truly wants out of life.

Having been a regular on "Saturday Night Live" for the better part of a decade, there might have been a risk in Molly Shannon going in broad directions better suited for a skit than a feature film. Instead, she welcomes the chance to stretch as an actress and play the material completely straight, an invaluable choice that proves what a first-rate comic talent she is. More than that, though, Shannon enlivens Peggy as a real and flawed character, her quiet, fish-out-of-water state transitioning to a newfound strength of character and grasp on her beliefs, no matter how crazy or outlandish some of them may appear. Not that Molly Shannon needs any support when she is in such command of the screen, but the rest of the ensemble—Regina King (2004's "Ray") as the gabby Layla; Laura Dern (2006's "Inland Empire") as the overly cautious Bret; Peter Sarsgaard (2005's "Flightplan") as the asexual Newt; John C. Reilly (2006's "Talladega Nights: The Ballad of Ricky Bobby") as hunting enthusiast Al; Josh Pais (2005's "Little Manhattan") as Peggy's awkward boss Robin—fill their roles with inspired aplomb.

As "Year of the Dog" heads into its third act and Peggy's actions become increasingly erratic and even scary, the film threatens to jump the shark. Much of the fun of the previous hour and change is replaced with a feeling of dread for Peggy's mental state, and it wouldn't be surprising for some viewers to question where things are going. Fortunately, it is all at the service of director Mike White's master plan, and the concluding scenes reign in the narrative hiccups for a finale that is emotionally satisfying, truthful and just about perfect. "Year of the Dog" is a charming slice-of-life that embraces Peggy's quirks and loves her for them. By the end—long before the end, actually—we do too.