"A Christmas Carol," adapted by Tom Frey, opened Friday at the Historic Iao Theater to a more than large and friendly crowd. The theater was festively decorated and the unique set, designed by Caro Walker, was in itself a gigantic piece of art. Sitting centerstage is a London street scene which doubles as an advent calendar. Doors and windows open to reveal the face of Jacob Marley, stools, desks and Scrooge's bed. Flanking the advent flat are two Currier-and-Ives-like 12-foot Christmas Cards. The wonderful period costumes were made, not rented, by Linda Timms, most of them created from scratch. Alexis Dascoulias' simplified version puts all the focus on the cast, thereby requiring the actors to be present, consistent and believable. Musical Director Robert Wills asks the same of his a capella choir, all of whom shift in and out of scenes playing multiple characters throughout the show.