It's the richness in their voices that makes them a little darker, maybe a bit more complex than the fluty sopranos, which is why the mezzo-soprano characters are often the villains or the sages. Or, famously, the dancing gypsy hottie stirring up trouble in Georges Bizet's "Carmen," kicking off the Virginia Opera's season at the Landmark Theater Friday, Oct. 20, at 8 p.m. and Sunday, Oct. 22, at 2:30 p.m. She's the original club girl, the one who just wants to dance under the swirling lights while guys in silk V-necks try to buy her lemon drops. Two such guys in 1830s Seville are the soldier Don José and the bullfighter Escamillo, following the rose-throwing Carmen, played by Christina Nassif, all over the stage as she falls in and out of love with them, driving the soldier mad with desire as she dances toward the fate she's known about since before she even came into this club. Tickets are $15-$85. Call 262-8100 or visit www.vaopera.org.