And Soon the Darkness (1970)

And Soon the Darkness (1970), directed by Robert Fuest.

A slow-burn thriller about two English girls on a cycling trip in France. Foolishly, they split up after an argument and one vanishes along a stretch of rural road known for rape-and-murder. Her friend searches for her but doesn't speak the language and is not getting much help from the locals. It builds to the type of climax familiar in later slasher films.

I had never heard of this until it appeared on Blu-ray. It is a small film but I think rather well done. Points of interest:

Available on Blu-ray from Kino with two commentary tracks: production memories by the director and producer, and a happy appreciation by film scholar Troy Howarth.