For most audiences under the age of fifty, they will more than likely walk into "A Prairie Home Companion" having never heard of the same-titled radio show on which it is based. They almost certainly will have never actually listened to it, and maybe that's the whole point. Introspective, intimate and powerfully low-key, the film is set in the present, but about the widely shifting tides of time and habit, happening in the now, but embroiled in memories from the past. For renowned filmmaker Robert Altman (2000's "Dr. T and the Women"), "A Prairie Home Companion" strikes a resounding, deeply personal chord. At 81 years of age and shaky in health—Paul Thomas Anderson reportedly was on standby during filming in case Altman could not fulfill his directing duties—Altman has made a gentle, bittersweet motion picture about things that could very well be on his mind, like coming to terms with one's own choices in his or her life while recognizing the inevitabilities of mortality. At this stage in his illustrious career (1975's "Nashville" 1977's "3 Women" and 1993's "Short Cuts" rank at the top of his résumé), there couldn't be a more fitting melding of artist and material.

For over thirty years, a bouncy, old-fashioned, down-home radio program called "A Prairie Home Companion" has stood the test of time, finding a devoted listenership even as the style and state of radio has changed dramatically. That time, alas, is finally coming to an end for the hardworking backstage staff and passionate on-air personalities at St. Paul, Minnesota's Fitzgerald Theater, who have only one more show to do before the place is bulldozed to make way for a parking lot. As the program marches forward, host Garrison Keillor (playing himself) puts up an air of denial, and the rest of the talent, like singing sisters Yolanda (Meryl Streep) and Rhonda Johnson (Lily Tomlin) and country-western duo Dusty (Woody Harrelson) and Lefty (John C. Reilly), prepares to bid their farewells, a mysterious blonde (Virginia Madsen) arrives on the scene with a curious tie to the show and an ulterior motive that will put into perspective the thin line between life and death.

"A Prairie Home Companion" has been written by creator and host Garrison Keillor, mixing factual people and fictional characters, and who better to know the behind-the-scenes ins and outs of a real radio show than him? Solidifying the material's treatment is director Robert Altman, a maestro when it comes to getting naturalistic, seemingly improvisational performances out of his actors. Together, Keillor and Altman have created a self-contained world so peppered in nuance, detail and exacting human interactions that viewers do not need to have listened to or heard of the title program to be actively swept up. All they need to know is right there on the screen, from the lovable group of misfits and faded stars putting on halfway believable game faces despite being frightened beyond belief where their lives are headed next, to the moving, unforced depiction of a professional family facing an abrupt break-up.

Little happens in the way of major point-A-to-point-B plot developments—save for the opening and closing scene, the picture never journeys beyond the stages and dressing rooms of the Fitzgerald Theater during the final broadcast of "A Prairie Home Companion"—and yet the film is richly rewarding and layered on a more thematic level. Even with audiences dwindling and the end in sight, the characters cling with nobility to remembrances of their glory days and hopes that their work still means something to someone somewhere. This show, after all, is what they do best and what they have put their life's blood, sweat and tears into. And, when a death unexpectedly occurs among them, the program's "show-must-go" mentality is best summed up by host Garrison Keillor, who declines in paying his respects on the air: "At this stage of my life, if I gave a eulogy for every person I knew who died, I'd be doing nothing else but giving eulogies."

There isn't a false note struck by the actors, and how could there? The cast is uniformly excellent, even when the characters aren't exactly mapped out as three-dimensional. Kevin Kline (2004's "De-Lovely") plays Guy Noir, a security worker for the show and occasional narrator of the film, as a serious-faced private eye straight out of the '40s whose very name is no accident. Kline digs his nails into the part and the fun he's having is readily apparent. Meryl Streep (2005's "Prime") is brilliant as usual, bringing her skills as a chameleon and hidden singing talents to the forefront as Yolanda Johnson, one-half of the surviving members of an all-sister musical group. She and Lily Tomlin (2004's "I ♥ Huckabees"), as sister Rhonda, delightfully play off one another with the effortless back-and-forth and emotional depth of actual siblings. The moments in which they reminisce about their beloved mother and sisters, all now deceased, are some of the film's most real and powerful. As singing partners Dusty and Lefty, Woody Harrelson (2005's "North Country") and John C. Reilly (2005's "Dark Water") are also a dynamite pairing, trading off salty barbs and coarse jokes during their song performances with expert comic timing.

In unforgettable supporting work, Virginia Madsen makes good on the promise of her Oscar-nominated work in 2004's "Sideways"—she can be forgiven for her thankless participation in 2006's "Firewall"—as a mysterious presence whose angelic appearance could be one of either danger or mercy. On paper, Madsen's difficult and obscure role would seem an impossible one to portray, but she nails it, stealing all of her scenes and wholly believable, to boot, as the person she ultimately is revealed to be. As pregnant, by-the-book stage manager Molly, Maya Rudolph (2004's "50 First Dates," TV's "SNL") is a veritable deadpan hoot, trying to no avail to keep the show running smoothly amid co-workers who scarcely realize she's there. Finally, Lindsay Lohan is ten times better here than she was in 2006's awful "Just My Luck," reaffirming that her talent isn't what is in question, but the material she takes on is. As Lola, Yolanda's suicide-obsessed, poetry-writing daughter, Lohan blends in nicely with the rest of the ensemble and, like many of her older, more experienced co-stars, runs with the opportunity to perform a song live onstage—in her case, a darkly spun version of "Frankie and Johnny."

With showstopping musical performances aplenty—Meryl Streep's are particular highlights—and the pace kept hectic and involving to match what it is really like to work on a grand-scale radio show, "A Prairie Home Companion" breezes by. As entertaining and light as any solid radio broadcast, the film gets big laughs in its clever, rapid-fire delivery and finds beauty and wisdom within its narrative simplicity. Only the final scene has a tacked-on essence, and might have been better to have been dropped. The suggestive last couple of shots, especially, put a spin on the conclusion that felt unnecessary in light of all that had come before. Nevertheless, what director Robert Altman brings to "A Prairie Home Companion" is most invaluable of all: a sense of laid-back, incessant comfort and nostalgia, akin to hanging out with a group of old school chums for 105 minutes, thinking back on days past when things were, if not simpler, more open to possibility. It's never too late, though, Altman urges, until it is.