I am glad I managed to see this on what was, sadly, its last day. I was put off by reviews which said it was about the American justice system when it is actually a very well acted psychological interplay between the two central characters. The prison setting is a great way to do this as it pushes together people who might well wish to be elsewhere, e.g. Bully Boy at the St James Theatre last year, or classic comedies such as Porridge and Steptoe & Son.
I am only bothering to write this review as I hope this play gets another run and it is such a shame this one is over.