The film contains references to real historical events, and Campion has stated that he based the story on the German occupation of the Channel Islands. Guernsey's history of witchcraft and the occult includes the existence of the "Bad Books" (books of black magic), and copies can be found in two libraries in the Channel Islands. When Grogan and Tane hear screaming from within the fortification, Grogan thinks it is other allied commandos who are being tortured, stating, "You know what they did to Blondie's men in Bordeaux", a reference to the torture of captured Royal Marines during Operation Frankton under the command of Major Herbert 'Blondie' Hasler. As Meyer ties Grogan's thumbs with a piece of wire to torture him, Meyer talks about the Allied "gangster commandos, who raided these very islands and killed innocent German prisoners with their hands tied behind their backs", which is a reference to Operation Basalt, a British Commando raid on Sark during which a German prisoner was shot dead whilst his hands were tied, which in turn led to Adolf Hitler issuing his Commando Order, upon which the torture scene in the film is based. When Meyer is attempting to interrogate Grogan, he taunts Grogan's New Zealand background: "New Zealanders, a bunch of farmers driving around the deserts of North Africa, attacking by night and fleeing to hide like cowards", which is a reference to the New Zealand section of the Long Range Desert Group. Meyer also taunts Grogan by insulting the Maoris of New Zealand, which he describes as "the descendents of cannibals and headhunters", which is a reference to a 1940s German radio propaganda broadcast.