Hamlet calls death "that undiscovered country from whose bourn no traveler returns." But he's wrong. Some do return. Each night after the applause dies, the curtain falls, the audience vanishes, the cleaners dust, and the lights are killed, great theatres become dark and silent places. But not always quite empty. That's when the theatre ghosts make their entrance and strut and fret their hour upon the shadowed boards, illuminated...