Island at War asks us to spend seven and a half hours on one of the Channel Islands, to get a tactile reading on just what a Nazi occupation felt like. After consulting reams of history and reminiscence, playwright and television writer Stephen Mallatratt (who sadly died last month) has fictionalized a “St. Gregory,” where a civilian population of tomato growers must endure a German military presence that features sexual exploitation and anti-Semitism. The English behave a bit better, though there are nice types and bad apples on both sides. With fine actors like James Wilby and Saskia Reeves and talented newcomers like Louisa Clein and Samantha Robinson (a local chanteuse), Island at War is reasonably absorbing but no great classic.