What happens when the actors and the characters they portray get all mixed up? You get Rupert Holmes' clever and bizarre "Accomplice," a murder mystery in which the murder is unclear, and so is the mystery of it.

If that seems like total confusion, it's supposed to – Holmes is nothing if not sly in the unusual route he takes in plotting. The all-around British artist – a singer and composer as well as a playwright and director – is also the writer of "The Mystery of Edwin Drood," the goof that did well in a revival on Broadway last season.

Isis Productions is staging an amusing "Accomplice," about two couples with conflicting and sometimes funny ulterior motives. The show's hard to bring off, because almost the entire first half calls for acting that falls somewhere between acceptable and questionable, for reasons that become clear only later in the evening. Sitting there without a clue, you're prone to think initially that something's missing from the performances, when it's not. The 1990 play won't work unless it stymies the audience at times – and audiences don't especially appreciate confounding theater.

In the second half, when the play allows us to tie together loose knots, "Accomplice" becomes a pleasure – a nasty one, since we've been put through the ringer trying to figure it out, but satisfying in any case. Neill Hartley's direction on the fifth-floor of the Walnut Street Theatre takes advantage of the play's confusions – he never lets you think too much or too long about what's real and what's not.

The cast is excellent. Mark Knight is the standout here, in two major roles that allow him to employ his gift for what seems like nonchalant comic delivery. Renee Richman-Weisband, the producing artistic director of Isis Productions, joins Kirsten Quinn and Rob Hargraves to carry out the convolutions.


"Accomplice," produced by Isis Productions, runs through March 30 at the fifth-foor stage of Walnut Street Theatre, at Ninth and Walnut Streets. www.isisperforms.com.