The game of Clue is about different people who gather for a fateful evening only to discover they are all suspects in a murder. The entertainment value comes from finding out whodunit.

Like the game and subsequent film version of Clue starring Tim Curry, Gosford Park has a similar theme. However, the entertainment doesn’t stop when the twisted, murderous plot is eventually unfolded.

Director Robert Altman tells his tale of rich, British snobs and the servants who tend to them like a tailor would diligently sew a pair of trousers: seam by seam. The film’s two settings take place above and below the stairs of an old, English country estate. While the upper class is gathered for a weekend shooting excursion, the real action takes place in the basement with the butler of the house and the valets to the houseguests in this deliciously funny commentary on British society in the 1930s.

But Altman’s light comedy-mystery is not for all tastes. A costumed period piece that sometimes plays like a Merchant-Ivory knockoff yawner, Gosford Park is slow to get to its point but well worth the wait.

An all-star cast helps move the story along, especially since co-screenwriters Julian Fellowes and Bob Balaban give each of them a complete character to play with.

At first, we are introduced to the valets below the stairs as the guests arrive. Each servant takes on the name of his or her employer to avoid confusion. Nuances like this are provided to note that servants are so meaningless in that society and therefore have plenty of reason to act almost as snobbishly back to their masters.

However, like a symbiotic relationship, the servants are only as important as their narcissistic masters allow them to be. That theme is resonated when Elsie (Emily Watson) is dismissed from the house after a discretion is made indiscreet.

But in the life of aristocrats, indiscretions are what make life interesting. And as one servant tells another in the film, “We all have our little secrets,” it is how these actors reveal them that makes the film worth following.

The cast is led by Kelly Macdonald (Trainspotting), who plays lady’s maid Mary to the arrogant Constance (Maggie Smith). Constance’s brother, Sir William (Michael Gambon), is the head of the household who brings everyone together for the holiday. The rest of the party is comprised of William’s young, saucy wife Sylvia (Kristin Scott Thomas), famous film star Ivor Novella (Jeremy Northam) and American Hollywood producer Morris Weissman (Balaban). Ryan Phillippe and Clive Owen (Croupier), whose characters each have a few secrets of their own, play Ivor and Morris’s valets. Richard E. Grant, Helen Mirren and Derek Jacobi round out the all-star British cast, which in their small roles, provide enough richness to set Park’s ensemble apart from other films made today that use almost-meaningless characters as filler.

Such is not the case for vets like Watson and Smith. Smith’s Constance is so convincing in her insolence that you almost want to reach through the screen and slap her. And Watson’s sweetly cynical Elsie is so courageous throughout her plight that you feel warmth in her character as she is almost completely surrounded by coldness. But Mirren takes the cake for squeezing every inch out of her Ms. Wilson role. She turns an otherwise supporting player housekeeper into a complete character.

But Gosford Park itself succeeds by squeezing in every joke and bit of energy available to make full use of its singular setting. And when it’s over and all the characters exit the house, you don’t want to leave your seat.

• Gosford Park is Rated R