A very proper butler in striped pants enters the drawing room of an English manor house as the curtain rises, and Dame Agatha Christie is up to her old sleight-of-hand tricks on the stage of Olney Theater.

It's become a summer-season tradition at Olney to stage a Christie puzzler, and this year it's "Black Coffee," which the Grand Dowager of Crime wrote back in 1930 as her first original play.

You can't write "Witness for the Prosecution" or "The Mousetrap" every day, and "Black Coffee" certainly isn't in that class. But everyone likes the challenge of an ingenious puzzle. The Olney production adds a large dollop of humor to the formularized characters and cliches. "Black Coffee" comes off as a light sugar-and-cream entertainment of summer theater.

The Christie mystery wil run at Olney for the next three weeks, through July 9.

Dame Agatha herself, in her autobiography, writes a concise review of her first play: "It was a conventional spy thriller, and although full of cliches, it was not, I think, at all bad."

As it turns out, after a lagging start, "Black Coffee" has rather good moments. There are several stylish performances with just the right tone of mocking fun to handle lines such as: "I'm like a fly trapped in a spider's web."

If the plot's the thing in a Christie puzzle play, "Black Coffee" does have the added enticement of Hercule Poirot, the dapper, vain, brainy little Belgium detective. Robert Symonds carries off Poirot, to the twirl of his waxed mustaches, his shiny patent leather shoes, and such egotistical utterances as: "It is impossible to deceive Hercule Poirot."

People do try to deceive Monsieur Poirot. In "Black Coffee," Hercule is summoned to Abbot's Cleve, the manor house of Sir Claud Amory, an eccentric gentleman-inventor who has a formula for an explosive atom-smashing process (this was written in 1930). The formula has been stolen from the safe, and Sir Claud gives the thief the honorable chance to return the formula during a few minutes of darkness in the drawing room.

It would be cavalier to reveal any more of the plot.The only hint is that Poirot's obsession with neatness and symmetry helps solve the puzzler.

Along with Poirot of Symonds, the production sparkles with the performance of Joan White, who turns Sir Claud's spinster sister into a delight, with her wandering anecdotes and her wool-gathering lines, even as she knits.

"I'm so glad that I ordered fried sole tonight. It was one of his favorite dishes" says Aunt Caroline after learning that her brother has been poisoned.

The other performers add special touches to enliven the play's cardboard characters - Gwyn Gilliss as the fetching, mod Jazz-Age niece; Mary Anne Dempsey, at times overwrought as the Italian-born daughter-in-law of Sir Claud; Rudolph Willrich as the son; Daniel Szelag as the bright confidential secretary; David Little, as the mysterious Dr. Carelli from Italy, and Michael Rothhaar, who manages to rescue the thankless role of Capt. Hastings, the Watson foil for Poirot.

"Black Coffee" was produced in 1934, when Dame Agatha had made her splash as a mystery novelist. It lasted four or five months on London's West End theater section. Daniel R. Heller, Olney's associate producer, dug up a copy of the play in the Luce Library at Catholic University. As far as he can determine, this is the American professional premiere of "Black Coffee."

So it's no "Mousetrap," which has been running since 1952 on the London stage. But it's fun to play the game with Dame Agatha in this play from the Golden Age of mystery, before psychological realism intruded on the game of wits.