The story is based on events taking place between between mars 1979 and October 1980, when several people were killed in France, Italy and Germany by the underground organization named Fédération d'action nationaliste et européenne (FANE), aka Faisceaux nationalistes-européens (july-October 1980), supposedly consistent of right-wing police officers who considered the judicial system too bland against criminals and communists. The organization announced its dissolution, but the French courts dissolved it in 1985, and again in 1987 due to judicial errors in the first decision. The French police branch of FANE was known as "Honneur de la police", hence the film's expression "Fidélité à la police". One of their victims were people affiliated to the left-wing movement "Prima Linea", referenced in the movie as "Prima Cosa". Coluche may have been one of Honneur de la police's victims.
The building used in the movie is the Gothic, Grade II listed Barnes Hospital in Cheadle, Cheshire UK. The building, which once topped a list of the '15 creepiest abandoned places in Britain', has a colourful past that includes being this films location.
The film's title is a play on words of the French saying, "ne réveillez pas le chat qui dort" that corresponds to the English adage, "let sleeping dogs lie".