On Christmas Eve 1914, the trenches of the First World War’s Western Front were largely quiet as a widespread, unofficial ceasefire took hold. Soldiers on both sides of the conflict buried their dead, traded prisoners and sang carols. In some places, the no-man’s-land filled with erstwhile enemies exchanging gifts, sharing food and playing soccer. Made all the more stunning by the years of crushing violence that followed, the Christmas Truce is the subject of All Is Calm, an a cappella chamber opera presented by Opera North for just two performances at the Lebanon Opera House.