In the 1940s a teenage Brendan Behan (later one of Ireland’s finest poets) did a stretch in England’s Borstal Prison for working for the I.R.A. Director Peter Sheridan (who co-wrote the script with Nye Heron) recounts Behan’s jail term in a crisply paced and well-acted film. The credits, however, say that it’s only “inspired by” Behan’s book, and not every detail rings true; there are also minor but unmistakeable anachronisms that work against it. The film is saved by its performances: Michael York (who seems to be turning into James Mason) as the warden, Eva Birthistle as his daughter, Danny Dyer and Robin Laing as Behan’s fellow inmates. Best of all, easily carrying the film, is Shawn Hatosy as Behan himself, growing subtly from callow youth to adulthood over the course of his sentence.