[4] The film is about two detectives who investigate a series of grisly murders in and around an isolated university campus in a deep valley of the French Alps.

Detective Superintendent (Commissaire Principal) Pierre Niemans (Jean Reno), is sent to the small university town of Guernon in the French Alps to investigate a brutal murder.

Dr Cherneze (Jean-Pierre Cassel), explains that the school's isolation led to inbreeding amongst the professors, with increasingly serious genetic disorders.

Coincidentally Detective Inspector (Lieutenant de Police)[6] Max Kerkerian (Vincent Cassel) is in the nearby town of Sarzac investigating the desecration of the grave of Judith Herault, a girl who died in 1982, and the theft of her photos from the local primary school.

The mother tells Kerkerian that at the faculty's hospital in Guernon, they were attacked by "demons" on their way back and when they fled, her husband and her daughter were killed in the road accident.

Sertys, they deduce, must have swapped Fanny for one of the dead faculty babies while leaving her identical twin, Judith, with her birth family as a control subject.

Exteriors were shot on location near Grenoble in the communes of Albertville, Livet-et-Gavet, Avrieux, Apprieu, Bourg d'Oisans, Vallorcine, Vinay and Virieu sur Bourbre.

The glacier scenes were filmed on the Mer de Glace beneath Mont-Blanc and above Argentière in the Chamonix Valley, Haute-Savoie.