Sure, many people find the holidays depressing, but at least you're not a functionally alcoholic Dublin undertaker whose estranged daughter shows up on Christmas Eve with disturbing news. That's the grim premise of Conor McPherson's Dublin Carol, now playing the Steppenwolf Upstairs Theatre. William Petersen (CSI) exudes humanity in the disconnected, world-weary lead role. McPherson, meanwhile, is cornering the market on downcast holiday drama; next up at Steppenwolf is his Tony-nominated The Seafarer, another long, dark Christmastime of the soul.