The best blues always is a little frightening: As the greats pour their soul into a cathartic purging, a listener often is just a little bit worried that all of that pain and anger might backfire in their direction.

As tens of thousands of revelers once again filled Grant Park for the Blues Festival over the weekend, precious little on the bill there held that kind of promise -- or threat. For those kinds of thrills and chills, you had to see PJ Harvey and John Parish at the Riviera Theatre Friday night.

To an even greater degree than on her own stellar albums, British singer Polly Jean Harvey has felt free to inhabit a wide range of characters struggling with all manner of crises on the two discs she's made with multi-instrumentalist Parish: "Dance Hall at Louse Point" (1996) and the recent "A Woman a Man Walked By."

Rather than shouldering all of the songwriting burden, in this collaboration, Harvey crafts the vocals and lyrics based on inspiration from Parish's music. And her at-times wordless singing is much more subtle, nuanced and alternately beautiful and harrowing.
While some longtime fans may have been disappointed that Friday's set list shorted the rest of Harvey's rich catalog in favor of the two albums with Parish, the rewarding range of her singing and the intensity of her performance were undeniable, whether she was gliding through entrancingly moody tracks such as "Black Hearted Love" and "Rope Bridge Crossing" at the start of the night, or pounding through furious stompers like the Captain Beefheart homage "Pig Will Not," which closed the set proper preceding the well-deserved encore.

The backing group in fact included a Beefheart alum, bassist and keyboardist Eric Drew Feldman, in addition to Jean-Marc Butty on drums and Giovanni Ferrario on guitar. As with the best of the Captain and his Magic Band, Harvey, Parish and their group created a merger of blues and rock that was both futuristic and timeless.

The forlorn melodies and fractured grooves were an ideal setting for Harvey's emotional vocals and theatrical delivery. And if the latter was less flamboyant than during the height of the alternative era, it was dramatic nonetheless.

During a fierce version of "Taut," Harvey started out on her knees as if in prayer, and wound up stalking the stage like a woman possessed. "Save me, Jesus!" she screamed. And you had to hope He heard her.