Going crazy is not supposed to be this much fun.

At the Spreckels Center, two distinct shows about darkness and insanity have just opened: one, a musical adaptation of a literary classic; the other, a squirm-inducing cult-sensation.

Jekyll & Hyde: The Musical, directed by musical-theater veteran Gene Abravaya, tells the story of a good-hearted doctor whose pioneering science projects split his soul into two. Based on the book by Robert Louis Stevenson, the Spreckels production features a cast of North Bay regulars and includes the welcome Sonoma County return of power-throated Kelly Brandeberg, back for a visit after a long sojourn in New York City.

Dr. Jekyll (John Shillington) is desperate to understand how the human mind breaks down into madness. Believing the answer can be found in the natural duality between good and evil, he concocts a serum that will divide the mind into its good and bad halves. When the board of the local hospital laughs off his request for support of his research, he becomes his own guinea pig, alarming his friend Gabriel (John Rathjen) and his fianc–e, Emma (Heather Lane).

Transformed into an amoral libertine, exulting in his sense of newfound freedom, the doctor—as Mr. Hyde—launches a murderous reign of terror against the hospital directors. Caught up in the storm is Lucy (Brandeberg), an abused young saloon singer who falls for the kind Jekyll, while unknowingly becoming the object of Hyde's desire.

The large cast is strong and in fine voice, more than compensating for some weak tunes and a good deal of silly melodramatics. Jekyll & Hyde is good pop-opera fun, a welcome surprise this Halloween season.

Meanwhile, in Spreckels' small Condiotti Theater, Narrow Way Stage Company presents Tracy Letts' outrageous comedy-drama Bug, directed with verve and passion by Lennie Dean. The first work by Letts, who won the Pulitzer for August: Osage County, the brilliantly demented Bug requires a rare commitment from its actors (intense performances, blood-spurting violence and lots of full frontal nudity), and this cast brings that commitment, and plenty more.

Agnes (Jessica Short) is a lonely waitress with deep emotional scars and a crippling self-hatred she's trying to overcome. When she meets Peter (John Browning), a shell-shocked Gulf War vet with gradually emerging paranoiac tendencies, Agnes is gradually pulled into his convincingly detailed delusions.

Or are there really infinitesimal carnivorous aphids in Agnes' hotel room? Perhaps Peter really is a refugee from a sinister government experiment to imbed robotic transmitter bugs under his skin, as he insists. It's possible that Agnes' best-friend R. C. (LC Smith) and bullying ex-husband Jerry (Matthew T. Witthaus) truly are part of a CIA conspiracy to recapture Peter, as Agnes eventually comes to believe. And if the mysterious Dr. Sweet (Samson Hood) really is looking out for Peter's welfare, why is he acting so . . . weird?

Part love story and part freak show, Letts' magnificently plotted script is a mesmerizing look at two damaged souls whose union both saves and undoes them. The splendid sound design by Doug Faxon and the perfectly seedy set by Tony Ginesi are practically characters themselves.

Definitely not for the squeamish, Bug is a must-see for its full-throttle performances. Though it takes its audience to very dark places, the aching honesty of its deeply human story is strangely powerful, deeply moving and entirely unforgettable.

'Jekyll & Hyde: The Musical' runs Friday–Saturday, Oct. 28–29, at 8pm, and Sunday, Oct. 30, at 2pm; $24–$26. 'Bug' runs Thursday–Sunday through Nov. 6; Thursday–Saturday at 8pm, Sundays at 2pm. Both shows at Spreckels Center, 5409 Snyder Lane, Rohnert Park. 707.588.3400.

Send a letter to the editor about this story.