Demons at Midnight (1961)

This drama's main asset is Charles Boyer as Pierre, a father out looking for his son one night. Pierre receives a call from a woman who says she will kill herself because of his son. Naturally disturbed at this news, Pierre takes off to find his son and avert disaster. Along the way, he picks up a malcontent, wealthy young woman who decides to stick with him and help him look for his son. After traveling through some of the worst aspects of Paris' demi-monde, Pierre begins to wonder if his son will ever be found. Meanwhile, the relationship with his newfound wealthy friend is heating up.