On Blueberry Hill sounds like a musical but it’s a sombre prison drama set in Ireland. Two bunkbeds. Above, an older man, Christy. Below, his younger companion, PJ. They take turns to talk, and gradually they reveal how their lives are interwoven. These are men of unusual intelligence and articulacy, and both are so profoundly in love with life’s simplest joys that their incarceration seems barely credible.