The cast of FX's "It's Always Sunny in Philadelphia" will be live at the Beacon Theatre on September 16th, performing their musical "The Nightman Cometh." Based on the fan-favorite episode, "The Nightman Cometh" is a full-length musical featuring cast members Rob McElhenney (Mac), Charlie Day (Charlie), Glenn Howerton (Dennis), Kaitlin Olson (Sweet Dee), and Danny DeVito (Frank) with special appearances by Mary Elizabeth Ellis (The Waitress) and Artemis Pebdani (Artemis). Following the performance, there will also be a screening of new episodes from the upcoming season of "It's Always Sunny in Philadelphia" on FX.