Many marriages reach a turning point when the partners regard one another not as "darling" but as "companion," or worse. "Darling Companion" concerns a couple who have been teetering on that plateau for years. Diane Keaton plays Beth, an empty-nester who rescues an abandoned collie from a Denver freeway and finds the unconditional love that has been absent from her life for years. Kevin Kline plays Joseph, her professionally accomplished but distant surgeon husband, an aloof, proud show-poodle of a man.

Beth loves the dog, Freeway, more than she loves her husband. On a walk around their mountain vacation home, Joseph loses the pooch. The couple search for Freeway, get lost, deal with outdoors hardships and confront their relationship troubles. They find their path back home in better emotional shape than when they started.

This is not high-stakes adventure. The film's director, Lawrence Kasdan (who collaborated with his wife, Meg, on the script), has done that, better than anyone, as screenwriter of "Raiders of the Lost Ark" and "The Empire Strikes Back." This is a small ensemble comedy about the cross-currents of family life, loneliness inside a committed relationship, guilt, getting old, self-renewal.

There are houseguests who join the search party, and most are drawn with good attention to detail. Joseph's sister, Penny (Dianne Wiest), and her new boyfriend, Russell (Richard Jenkins), make an odd pair. He's got a scheme to open an English pub in Omaha with Penny's savings. Her adult son, Bryan, played by Mark Duplass, views Russell as an AARP gigolo. Bryan was sent to med school by his uncle and works with him; he seems to have inherited some of Joseph's control-freak tendencies. He overlooks the fact that his mom is glowing. Russell makes Penny happier than she's been in ages.

Russell, in a supporting role, is the movie's key. He's introduced as a dubious and dumb character. As we get to know him, we realize this un-pedigreed mutt of a guy is clever, loyal, brave, guileless and always up for an adventure. If he had a tail it would be continually wagging. Jenkins, an innately appealing performer, is irresistible here. The story, which argues that hope is more valuable than common sense, says you should give people a chance. They might not disappoint you.

If good intentions were everything, this benevolent film would be Best in Show. Alas, it's flawed by a drowsy pace (there is far too much hiking) and superfluous, ill-conceived characters. Sam Shepard plays the folksy sheriff who, like Kline's Joseph, senses that young bucks are about to shunt him aside. He occupies space on the canvas but doesn't add much color. As the vacation home's resident caretaker and hot-blooded Gypsy psychic, Ayelet Zurer is a gaudy stereotype from a bygone era. And what are we to make of the odd animated vignette in which poor Freeway is chased by snarling wolves?

There is no great plot to unwind here. You can guess for yourself (very easily) whether Freeway is saved. The story is kind of a mess, actually, a shaggy dog postscript to Kasdan's debut film as a writer/director, the zeitgeist classic "The Big Chill," where not a lot happened, either. It's about one family and lots of families, whose problems and personalities would not be big-screen material unless they were played by movie stars.