Fallen Angels has one of the best jokes of the spring theater season. It’s on Rose Byrne’s head. Photo: Joan Marcus An excerpt of this interview first appeared in Stage Whisperer , Vulture’s weekly newsletter for theater gossip, interviews, and more. Sign up here. The best sight gag of this theater season is a wig. Fallen Angels follows two women, Julia (Kelli O’Hara) and Jane (Rose Byrne), who have a ridiculous drunken night together. When Jane reemerges the next morning, her hair is