As a former regular on Saturday Night Live, Molly Shannon is part of her country’s comedy heritage. So it’s not just the uncanny physical resemblance that makes her America’s answer to Catherine Tate.

Indeed, Mike White’s doggedly indie comedy feels like an extended Tate sketch as Shannon’s spinsterish office worker Peggy gradually goes off the rails, much to the bemusement of the characters around her.

Peggy’s downward spiral begins when her adorable beagle Pencil is found in a bad way in neighbour Al’s garden. The mutt doesn’t make it. Peggy is shattered.

Her commitment-hungry workmate Layla (Regina King) - whose boyfriend is a sly dog himself - urges her to take her mind off the tragedy by going on a date with Al (Reilly). He seems like a nice guy.

It all goes well until Al declares his love… for hunting (sample philosophy on endangered species: “I figure you should get one before they’re all gone”).

Peggy is much more taken with committed vegan Newt (Sarsgard), the sympathetic but strangely reserved guy from the pet clinic. Persuaded into adopting a temperamental German Shepherd called Valentine, she takes Newt’s dog fostering campaign into the office. Her animal righteousness aroused, Peggy begins to step up her cause, forging her boss’s signature on charity cheques and – much to the horror of her child-obsessed sister-in-law (Dern) - exposing her niece to the grim realities behind films like Babe.

But another tragedy involving Newt and Valentine pushes Peggy into a mental barkdown whereupon our misguided hero rescues fifteen dogs from death row at the local pound. Save the Chihuahua, save the world.

White’s gently subversive script is closer in tone to his relationship comedy The Good Girl than his giddy collaborations with Jack Black. Played for chuckles rather than belly-laughs, it offers some thoughtful musings on the dark side of do-gooding.

Directorially, it’s an unremarkable and slightly self-conscious first effort. The sketchy feel is amplified by White frequently positioning his characters centre frame, mock documentary-style, and employing the sort of plinky-plonky mood music that accompanies so many indie comedies.

But with smashing performances and plenty of heart, it joins Bobcat Goldthwait’s recent Sleeping Dogs as a worthy addition to 2007’s woof-and-ready hall of fame. Elliott Noble