As a novelist and playwright, Agatha Christie was a master watchmaker. And much of the pleasure in her works comes from watching the clockwork unspool.

That clockwork nature is one reason her plays continue to be performed frequently. Her dramatic machines, once wound, will tick forward in an entertaining manner with little needed to keep them going, except a minimal set and serviceable performances.

McKeesport Little Theatre's "And Then There Were None," which opened Friday, offers more on both counts. But though this production kept ticking, it lost some of its impetus due to uneven performances.

Based on Ms. Christie's "Ten Little Indians," "None" brings 10 people of various backgrounds to an isolated, rocky island where they begin to die, one by one, according to methods described in a children's nursery rhyme.

Ms. Christie's critics have said her characters are usually no more than types, and "None" is no exception.

But these caricatures need to be performed with conviction, because their interactions supply the play's energy and logic. Many of the actors failed to clearly telegraph what types they were supposed to be.

Krissy Penn has a solid stage presence, but her governess, Vera Claythorne, seemed all of a giddy 17 -- neither as old nor as wise as the character demands.

Anna Marie Colecchi, who plays the self-righteous Emily Brent, seemed to be more of an impatient young woman than a pinched old biddy.

And while I put no great value in authentic accents, they were not appropriate for some characters. I had James Handley, as blue-blood cad Marston, pegged as a fishmonger for most of Act I. Jim Weldon, who plays Blore, had a lovely British accent, but he sounded too posh to be a retired police officer.

Aside from the accent, Mr. Weldon was thoroughly believable in his part, as was Bruce E. Travers as Dr. Armstrong.

The best performance is by Matthias Schonlau as the adventurer Lombard, especially in his lively take on the character's grave-side humor. And although Mr. Schonlau, who was born in Germany, sounds nothing like an Englishman, he does sound a bit like a South African -- where his character served in the military for many years.

Ryan Tierno, who stepped in when the original director dropped out, has designed an art deco set that's elegant and evocative.

Some of the flaws in this production are likely a consequence of that change, because it shortened the rehearsal period. The machine might have run more smoothly if it had been wound all the way up.

"And Then Were None" will run at McKeesport Little Theatre through March 16. Call 412-673-1100 for more information.