The Mourning is something of a departure for River North artistic director Frank Chaves: this duet shows the moment of death. "He doesn't want to let her go," Chaves says. "And she wants to let him comfort her--yet spare him suffering." He was inspired to create the piece (which Oak Park-based Momenta originally performed) by the music, a Russian ballad that starts out sounding like a pop love song but becomes something much more moving. The dancing evolves similarly: at first I thought The Mourning was yet another romantic duet, but the turns and swirls were so dizzyingly continuous as to become disorienting rather than conventionally lovely. Especially odd but evocative is a phrase in which the man spins the woman from front to back over and over near the floor. Tricky partnering also marks Paul Christiano's Balada para un loco, which last fall won an award for best new work, competing against several commissioned by the Dance Chicago Choreography Project. But Christiano's dance, unlike Chaves's, is often sculptural, featuring almost geometrical poses. Also new is a piece commissioned from Margo Sappington, whose work has often been performed by Hubbard Street Dance Chicago. In fact, the dance for seven women on this program, Unveiling the Curve, seems like a rethinking of her Step Out of Love, in which five women high-kick their way out of emotional entanglement. The emotional thrust of Unveiling the Curve is almost the opposite: the women start out hard and almost machinelike, then allow themselves to become pliant and vulnerable. Among several other company favorites being performed is Harrison McEldowney's clever 5 Easy Lessons, set in a ballroom-dance school. A jokey piece that at times requires the excellent River North performers to pretend they're bad dancers, it nevertheless ends on a highly satisfying kinetic note: frenetic movement to the lyric "slow down!" Harris Theater for Music and Dance, 205 E. Randolph, 312-334-7777. Through April 18: Friday-Saturday, 8 PM; Sunday, 3 PM. $25-$45.