The title--Surfer at the River Styx--kinda says it all: Twyla Tharp's often startling sextet intertwines mythic seriousness with pop-culture lightness. Donald Knaack's score begins with the melancholy sound of gongs struck randomly, but midway through he starts using traditional Asian instruments in rock arrangements. The choreography includes iconic, very formal stances that recall statuary, yoga, and the martial arts and movements that suggest hip-hop and roller-blading. The dramatis personae are two muscular heroes--one of them a surfer dude, the epitome of blond invulnerability to people of a certain age--and four subsidiary characters, two women and two men, who on one occasion stop to chat in what's obviously a gay confab. Though the story isn't very clear, the dancing clearly belongs in the same genre as Tharp's In the Upper Room: the point is energy and exhaustion, heroism and vulnerability. Fans will be happy to know that the piece is filled with Tharp's trademark quirky touches: little hopping walks, a slide into first. Also on the program--the first Chicago-area concert of Tharp's work since 1996--are Westerly Round, a piece that uses American folk dance and the ballet idiom set to music by Mark O'Connor, and a solo, Even the King, set to Johann Strauss's "Emperor Waltz." North Shore Center for the Performing Arts, 9501 Skokie Blvd., Skokie, 847-673-6300. Through February 1: Friday-Saturday, 8 PM. $48.