Theatre is slowly, tentatively opening up again and there’s no denying that a good play with however small a cast can deliver all the dramatic tension and tingle in the world. Joanna Murray-Smith’s Berlin comes with a hell of a title. Wasn’t that what Isherwood said goodbye to, isn’t that the name of one of Lou Reed’s grander and more austere concept albums? It’s no surprise that the play rehearses the shadows of modern German history and whatever the production turns out to be like (it opens 22 April) there’s no denying that the script with these two millennials crying...