The week in theatre: Unicorn; Churchill in Moscow " review
Garrick, London; Orange Tree theatre, RichmondErin Doherty, Stephen Mangan and Nicola Walker rise to the challenge in Mike Bartlett's witty dissection of a throuple. And Roger Allam makes a magnificent Churchill in Howard Brenton's broad-brush latest What a relief. After a splurge of jetted-in celebrity casting, here are two new plays buoyed up by on-the-spot, on-the-button stage actors. Every Mike Bartlett drama req…