Maybe now a little old-fashioned, “Forever Plaid” pays homage to the innocent boy bands of the ‘50s. The musical revue started Off-Broadway in 1990 and quickly gained loving momentum in fan’s eyes—so much so that it was made into a film in 2009. The hokey story centers on The Plaids, the recently deceased group that returns from the afterlife for one more shot at stardom. The musical presents some of the greatest hits from the ‘50s, but the best part is the magical four-part harmonies that come from this genuinely clean-cut show.