"The Sign of Four," a Sherlock Holmes thriller now at the Round House Theater, could alternatively be titled "The Case of the Lost Opportunity."

The play has enough going for it to make it baffling at first when things unravel. There's Douglas A. Cumming's set design and staging, both clearly the result of careful thought. And there are performances by Edward Trotta and Gerry Paone, who -- though no threat to Basil Rathbone and Nigel Bruce -- bring a measure of style to the roles of Holmes and Watson.

The main trouble rests in John Edward's new stage adaptation of Conan Doyle's story. It's a faithful and at times clever treatment that runs out of steam well before the end.

"I cannot live without brain work," Holmes tells Watson early on. The same might be said for the play -- which solves most of the mysteries in act one, leaving the audience scant reason to stay. The second act is all predictable resolution. It's a problem of pace and structure that won't go away, despite workmanlike acting and imaginative staging.

The story treats a treasure from India, ill- gotten and badly disposed of, and how it comes to haunt the heirs of two British officers. There's murder, betrayal and finally, as in most Holmes stories, the meting out of justice -- thanks, of course, to Sherlock.

The production uses "chamber" staging, a scaled-down style that more often suggests than displays. Paone, as Watson, often narrates the action -- "We were led through the doorway of a third-rate suburban dwelling" -- instead of showing it. A switch in rear-projected slides can make for a change in locale.

Most of the time it works, except when scenery is moved. The pieces, which resemble wooden railings and manage to evoke everything from a country manor to a police boat, grate against the floor -- a noise at once distracting and unnecessary.

The actors work hard. With a few exceptions, they take on several roles apiece -- with Martha Barber the busiest, variously playing Holmes' housekeeper, a murdered gentleman's housekeeper, a charter captain's wife and a fearsome Indian dart- blower.

Trotta, tall and severe, is a majestic Holmes, though he doesn't often burn with cocaine-sparked intensity. Smiling wryly at man's folly, he projects an apt sense of irony, and manages a good rapport with Paone as his earnest admirer. There's a bit of banter between them and some laughs here and there, but it's not enough -- and too elementary -- to hold your attention for the duration. THE SIGN OF FOUR -- At the Round House Theater through February 6.