Enter the Guardsman, Donmar Warehouse (0171-369 1732) 7.30pm

"You're going out there a youngster but you've got to come back a star!" Ruby Keeler danced a little, sang less and acted not at all, but boy, was she keen. She was also married to Al Jolson, which explains her presence as the ingenue in 42nd Street, the greatest of all backstage musicals. From Show Boat to Phantom of the Opera, the backstager is the musical's favourite form but Enter the Guardsman has a refreshingly different take on the idea. Instead of a bunch of overblown Busby Berkeley routines, it's a darkly theatrical tale of marital infidelity. With polymath Jeremy Sams at the helm, expect the unexpected.