Naked in the Night (1958)

Karin is a brilliant student whose good looks give her an added advantage in assuming the role of a prostitute and exploring Berlin's thriving sex industry. Hired posthaste by nefarious Madame Clavius, the pretty blonde sets about gathering information for her thesis when she discovers that her old friend Madeline has been financing her luxurious lifestyle by working as a call girl in the very same brothel. The situation turns sinister when Madeline reveals to Karin that she has fallen in love and longs to start a new life, but any girl who tries to leave Madame Clavius soon turns up dead. When Madeline admits to considering suicide, Karin hatches a plan for both of them to make a clean break from the brothel and avoid Madame Clavius' deadly wrath.