And Soon The Darkness (1970)

Robert Fuest’s And Soon the Darkness (1970), starring Pamela Franklin and Michele Dotrice, is a British suspense thriller about two young women cycling through rural France who encounter menace after one disappears. Mixing isolation, paranoia, and mystery, it has become a cult classic of British-European thrillers.

Från IMDB:
Two young English women go on a cycling tour of the French countryside. When one of them goes missing, the other begins to search for her. But who can she trust?