Archaeologist Mike Thompson is romantically linked to Margaret, the niece of Lord Drewell, a rich newpaper magnate and potential funder of Mike's next expedition. Unable to find a taxi one evening, Mike shares one with Ila, an attractive German woman. Later that night, Mike and Margaret are at a party when Margaret unexpectedly announces their engagement and he begins to feel trapped. His thoughts turn to the exotic Ila; he seeks her out and takes her to dinner, then back to his flat. When Margaret turns up unexpectedly, Mike gets rid of her and he is soon engaged in a passionate embrace with Ila.

The next morning, Mike calls her, hoping not to disturb her flatmate, a Miss Barker. But a Mr Barker answers the phone and Mike, furious to discover that she lives with a man, resolves not to see her again. However, unable to stay away, Mike accompanies her to the flat to meet Barker who, she explains, is her boss. Barker is a portly middle-aged American businessman who greets Mike in a friendly manner and takes him and Ila out to dinner.

Mike invites Ila for a weekend away and they go to a country hotel, posing as a married couple. While there, she gets a message from London and disappears; Mike's colleague David sees her in the pub arguing about money with a blonde man. When he confronts her, she tells him that the man is her brother.

Returning to the hotel, Ila tells Mike that her mother has died leaving debts and she needs £1,500; he tells her he can't get her that much money, so she tries to talk a wealthy hotel guest into giving it to her. Mike retires to bed, disgusted with her behaviour, and orders her to sleep in a separate room. The next morning, he wakes to find she has taken the early train; finding her keys on the floor, he follows her to London.

He goes straight to her flat and lets himself in. Finding her in bed with Reg Barker, Mike storms out. Reg calls him later and asks him over; he explains that he is love with Ila but the only way he can keep her is to let her have affairs with other men. She comes back, furious because the cheque Reg has written her has bounced. In her rage, she tells Mike that her 'brother Jack' is really her lover. Before leaving, she smashes Reg's most precious possession, a model ship his father gave him. Mike writes Reg a cheque to cover what Ila needs, but after Mike leaves, Reg burns it.

Ila arrives at a room in the shabby house where Jack is staying, bearing the news that Reg has shot himself. When Jack finds out she hasn't brought the money he needs, he walks out, saying he never wants to see her again.

At Mike's parents' house, a party is underway and Lord Drewell is speculating about the seedy background to the suicide of Reg Barker. Mike sees red and criticises Lord Drewell for digging up dirt about people, revealing that he knew Reg. Ila arrives and Margaret goes to talk to her; she asks for money in return for never seeing Mike again. Margaret calls Mike in but Ila denies attempting blackmail; when Margaret reveals that Ila has asked for £1,500, he realises she is telling the truth. Ila goes out into the night, knowing she's beaten.