Working with one of his trademark colliding-ensemble casts, whose chattering characters constantly step on each other’s verbal heels, Altman has adapted to the upscale environs without missing a beat, or an opportunity.

On the surface, "Gosford Park" is one of those familiar weekend-in-the-country affairs, in which the isolation of a group of distinct character types allows for the nurturing of a perfect microcosm — like bacteria in a petri dish. Midway through, there’s a murder, and an accompanying comic-relief detective, which shoves it another familiar direction.

But all this crisscrossing familiarity doesn’t breed contempt, thanks to Altman’s entirely distinctive traffic control measures.

The country estate belongs to Sir William (Michael Gambon) and Lady Sylvia (Kristin Scott Thomas) McCardle, who are also throwing the shebang, complete with afternoon shooting party.

Among the upstairs-invited are real-life British matinee idol Ivor Novello (a bemused and elegant Jeremy Northam), star of Hitchcock’s 1926 "The Lodger"; Lady Sylvia’s wizened and haughty aunt, Constance (Maggie Smith in full Maggie Smith throttle); Lord Stockbridge (Charles Dance), Lady Sylvia’s even haughtier brother-in-law; American film producer Morris Weissman (Bob Balaban), researching his impending production of "Charlie Chan in London"; and assorted other relatives and friends, almost all of them undergoing some kind of turning-point crisis.

And because this is also a tale of servants and those they serve, each guest gets a matching valet or maid, whose privileged points of view become those of the audience.

Altman’s readily obvious rule of thumb in the upstairs sequences is that at least one of the servants must be present as a witness to events. When the help regroups downstairs, the information is disseminated as needed — for them and us.

Down below, tending to the guests’ every needs (and we do mean every need), are the servers. Among them: McCordles’ head butler Jennings (Alan Bates); Mrs. Wilson (Helen Mirren), head housekeeper; Mrs. Croft ("Upstairs, Downstairs" alumna Eileen Atkins), the head cook; Probert, Sir William’s valet (Derek Jacobi); Elsie (Emily Watson), the head maid; George (Richard E. Grant), the head footman; Henry Denton (Ryan Phillippe), film producer Weissman’s Irish valet; Mary (Kelly Macdonald), cranky Constance’s maid; and Robert Parks (Clive Owen), brooding valet to Lord Stockbridge.

Armed with a stiletto script by Julian Fellowes ("Shadowlands") and employing a supple camera that rarely reposes, Altman goes to town, taking in the airs and pretensions of his social elite and filtering them through the lives of those below and on the sidelines.

Not a single member of the huge cast — right on down the line to the seemingly misplaced, all-too-American Phillippe as the insinuating Irish valet — fails to come through.

For serious cinephiles, Jean Renoir’s 1939 masterpiece, "The Rules of the Game" will immediately come to mind, especially around the time of the pheasant-shooting sequence, which, a la the fox hunt in "Rules," is staged to amplify the follies of the class at hand.

For television devotees, "Upstairs, Downstairs" will be the reference point, especially as the intrigue surrounding the relationships between served and servers begins to pan out.

And for the murder-mystery buffs lured in by the "whodunit" promise of the ad campaign, the wry specter of Dame Agatha Christie will doubtless be hovering in every nook and cranny, especially after the killing and the arrival of a quirky inspector (Stephen Fry) to sort it out.

Though some of the accompanying satire is anything but subtle (is there an easier target than the upper classes of a long-ago age?), the sheer liveliness of Altman’s complex orchestrations is the abiding joy of "Gosford Park."

If the murder, the motivations and the outcome all edge toward the obvious, the characters are rich enough to withstand it all — true intersecting denizens of an authentically chaotic Robert Altman repertory.

On the downside, but to no surprise to fans of Altman’s work, the movie is often hard to follow. His style of filmmaking involves entanglements of characters and subplots that don’t appear to have much to do with one another at first blush, and Gosford Park takes this to the next level. Here, the murder takes place at the climax of this confusion, leaving you rather disoriented in the middle of the 2-hour-plus drama. Fortunately, the tone loosens up when a comedy-dim police inspector basically gets nowhere in his investigation, but the pieces start coming together through the other characters. The good news is that it all seems to come together in the end in a way that didn’t require grasping every detail of every scene

Dan Craft and Dan Heller