This Could Be the Night (1957)

Straitlaced teacher Anne (Jean Simmons) needs extra work, so she becomes a receptionist at a swanky nightclub owned by mobster-turned-businessman Rocco (Paul Douglas), who seems tough but quickly shows his soft side. Before long Anne develops a crush on Rocco's partner, Tony (Anthony Franciosa), a swinging bachelor. Unfortunately, Tony thinks she doesn't fit in at the club and Rocco says she shouldn't get involved with him. Yet Anne is determined to show them both she can hang with their kind.