Owen O’Neill’s and Dave Johns’s play is, we are told, not an adaptation of the film, but of the Stephen King novella on which the film was based. But the fact that the fine American actors Kevin Anderson and Reg E Cathey look very much like Tim Robbins and Morgan Freeman in the movie, suggests that the producers of this prison story know who their target audience is. The leads’ performances are powerful, but cannot prevent Peter Sheridan’s production from feeling as if, rather than decades of brutality, the cons have merely endured a long evening — much like the audience.