I'm trying to write a new soul into the country!"

So declares William Shakespeare halfway through Bill Cain's magnificent new play Equivocation. The recent grand prize winner of the 2010 Steinberg/ATCA New Play Award, Cain's clever stab at historical fiction is a cape-and-dagger thriller set amid the homeland-security craziness of Jamesian England, not long after the thwarted "gunpowder plot" that would have destroyed Parliament and killed the king.

The play—a wonderfully sly mix of comedy, drama, literary observation and historical sleuthery—debuted last year at the Oregon Shakespeare Festival and has since been staged by companies all over the United States. The recently opened production at Marin Theatre Company in Mill Valley, directed by Jasson Minadakis, marks Equivocation's Bay Area premiere.

In the play, Shakespeare—called Shagspeare, or "Shag" by his friends—is a put-upon playwright, an artist whose works have made him wealthy but who hungers to do more than entertain. In an early scene, while his acting company is rehearsing a rough draft of the unorthodox King Lear, Shag (Charles Shaw Robinson) calms his nervous actors by explaining, "I'm trying to write a play that isn't about revenge—it's never been done!" Estranged from his wife, still grieving over the death of his young son and embroiled in a complicated relationship with his daughter, Judith (Anna Bullard), the dead boy's twin, Shagspeare is hungry for a real artistic challenge.

He gets it when he is commanded by Sir Robert Cecil, King James' merciless secretary of state, to write a new play describing the "official" version of the Gunpowder Plot. That current events were, at that time, not permitted onstage, is only a minor problem for Shag. What bothers him most is his suspicion that the government-sanctioned version of the story is a tissue of lies, thinly disguised propaganda designed to end speculation that there was, perhaps, no plot at all. Whether pro-Catholic conspirators did or didn't plan to kill the king, James' administration has been using it to confiscate property, imprison priests and justify the secret torture of government dissenters.

Stalling for time, Shagspeare begins interviewing the imprisoned plotters, and eventually sets himself a dangerous new challenge: to "write a new soul" into the country by telling the unvarnished truth—and somehow avoid being hanged.

Cain's delightfully complex play weaves numerous threads together without losing track of the story, which builds to not just one emotional climax, but two. As directed by Minadakis, a first-rate cast of six perform all the parts, with only Robinson and Bullard remaining in their specific roles. Andrew Hurteau, who plays Nate, one of Shagspeare's longtime actors, is especially good when he steps into the role of Cecil. Bullying, threatening and dripping with danger, he is also clearly a wounded man, suffering the indignities of being called "Beagle" by the insufferable Scottish king he himself placed on the throne.

Lance Gardner as the actor Armin is playfully chameleon-like in a number of supporting parts, and Craig Marker, as the hot-headed actor Sharpe, is brilliant, especially in a late scene where he plays the parts of King James and Macduff from Macbeth—at the same time. Andy Murray plays Richard Burbage, Shag's oldest friend and co-creator of the "cooperative venture" that is their acting company, also assaying the pivotal role of Father Henry Garnett. A Jesuit priest, Garnett was accused of masterminding the powder plot, but was already infamous for authoring a pamphlet on the doctrine of equivocation. Intended to help captured Catholics avoid punishment, equivocation was a method by which moral people could tell the truth and lie at the same time.

That desire, to speak the truth in difficult times, is what drives the actions of Shag's players, and what stands at the heart of this marvelous, inventive, beautifully presented show. Shagspeare yearns to write a play with a soul big enough to heal a nation. In Cain's Equivocation, it is not a country, but Shakespeare's fractured soul that is ultimately—and powerfully—saved.

'Equivocation' runs Tuesday–Sunday through May 2 at the Marin Theatre Company, 397 Miller Ave., Mill Valley. Tuesday, Thursday–Saturday at 8pm; Wednesday at 7:30pm; Sunday at 2pm and 7pm; Saturday also at 2pm. $34–$54; pay-what-you-can Tuesday. 415.388.5208.

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