Seven years after WWII, four women who worked as codebreakers at Bletchley Park have taken up mundane civilian lives. Susan, now a housewife, has collated data about a series of murders. She tries to convince the police she knows where another body is, but they are unable to locate it and dismiss her. Susan turns to her three friends. They work out where the next victim will be taken, find the body, then decide they are the only ones who can track down the hugger.
Utilising the statistics the women give the police three names and one is arrested when evidence is found. Meanwhile Jean and Lucy have discovered seven more murders linked where they believe innocent men have been convicted. The women devise a plan to trap the hugger using Lucy as bait but it backfires when she goes with the wrong man causing trouble in the personal lives of Susan and Lucy. Another suspect emerges from a top secret war department headed by Cavendish and Susan comes face to face with the hugger at a closed mental hospital.
Susan returns with the police but the hugger has gone. Susan finds a coded message in her home with Cavendish's address, and going there finds him dead. A postcard on Cavendish's desk provides a clue; and Susan, following the thread, walks alone into a trap set for her by the hugger. He attempts to hug her but is shot dead by the others, who followed her.