Ambitions unsatisfied, Castle began to make films independently. The inspiration of the 1955 French psychological thriller Les Diaboliques set the genre he would choose. He financed his first movie, Macabre (1958), by mortgaging his house. He came up with the idea to give every customer a certificate for a $1,000 life insurance policy from Lloyd's of London in case they should die of fright during the film. He stationed Nurses in the lobbies with hearses parked outside the theaters. Macabre was a hit.