A door opens, and the frantic, wild-eyed lady of the house stands there pointing a handgun at us. Blackout. Credit roll.

We’ll get back to that. We’re uninvited guests at a party at Janet’s flat in a tidy corner of London. The guests will soon arrive, and what a gang this is.

Don’t panic. This is no 1940-ish Ealing Studio chat and tea affair. Sex, guns, booze and drugs are here, and why would you leave a party with all of that and this cast?

We begin by spending several frames of this crazy, wild 71-minute film watching Janet’s hubby, Bill (a gnarly, bearded and wild-eyed Timothy Spall), sitting in a rickety chair in the living room, drinking his third large glass of wine, while listening to one of his LP jazz records.

This celebration party is for Janet (a sparkling, semi-hysterical Kristin Scott Thomas), who we learn is a British politician who has just been elected as England’s Minister of Health.

Janet, we learn right off the spot, clearly was born with her finger in the socket. Janet is the whirling planet around which all the other characters, the action and the tapas revolve around.

Janet will spend most of the 71 minutes dashing back and forth from the kitchen to the living room to the lavatory, and occasionally to the walled garden for a cigarette and a discovery.

We’re happy to see her best friend, April (a welcome Patricia Clarkson), here to oversee things and toss bundles of bon mots and assorted barbs around the room, like a female Oscar Wilde, in a sultry low-key voice. April is the calmest one here, and trust me, when you give Clarkson all the best lines, you’re in for a ride.

One by one and two by two, the guests arrive:

April’s husband, Gottfried, is here (a wonderful Bruno Ganz), who seems to have reached Nirvana as a new-age spiritual low-key guru.

But April and Gottfried are about to divorce, and we can see why. “Shut up,” April hisses; “Your cliches are unbearable,” Gottfried calms.

Janet’s lesbian couple arrive. This will be Martha (the great Cherry Jones) and her perky, bouncy younger wife Jinny (Emily Mortimer), who fancies white painter overalls and sneakers. The happy couple have good news. Jinny is pregnant; not with one, not two, but triplets.

Just as the group is digesting that surprise, a handsome, jittery American named Tom (a well-cast Cillian Murphy) arrives at the door, and immediately asks where the bathroom is.

Once in, Tom whips off his jacket, revealing a holstered handgun, and spreads out what appears to be a 6-foot line of cocaine on the base of the tub and snorts away. Let’s party.

Something clearly is bothering Tom, and considering the gun and cocaine, we can’t wait to see what or who it is.

His wife was expected, but she’s been “delayed.”

Tom for the first 10 minutes will be interrupted by Jinny, who dashes in to vomit in the toilet.

Meanwhile back in the living room, a flurry of words smash around, revealing all we need to know about each of the characters:

Bill, who has been drinking constantly throughout a barrage of revelations, has his bit of news to share.

“I’m dying.”

“What?”

“I’m terminal.”

And to add to his confession, he unloads a bombshell about his affair with the young wife of the handsome American in the toilet. Aha!

Basically, that’s all you need to know. Writer-director Sally Potter (“Orlando” and “The Tango Lesson”) will explain it all to you. Potter has a taste for extreme closeups, but here she has the faces for it.

The recipe is simple. Take one part each of Tom Stoppard, Harold Pinter, Luigi Pirandello and David Mamet, toss in a pinch of Monty Python, and stir well.

Don’t forget to put together the most perfect cast for such a thing, and you have a perfect Mishegas lasagna.

Potter’s script and direction blows hot and cold, but always steady. If only some American directors, I won’t mention names, knew how to make a 71-minute black comedy like this, I’d be happy.

J.P. Devine, of Waterville, is a former stage and film actor.