When her undercover CID officer brother is run down and killed by a car while investigating a diamond smuggling racket, his sister, Lynne (Maureen Connell), wants justice.
Detective Inspector Willoughby (Anthony Oliver) says there are no leads, so Lynne offers to investigate on her own, on the understanding she’ll report any leads to the pipe-smoking DI.
She takes a job at a Soho nightclub owned by the crime lord Nicky Venning (Alan Tilvern) where she strikes up a relationship with the club manager Sam Warren (Bill Nagy). She overhears Venning and his men planning a jewellery raid and tips off Willoughby and the would-be robbers are caught in the act.
Meanwhile, Venning orders the murder of Francine (Sonya Cordeau), a French dancer at his club, who became jealous of his interest in Lynne and threatened to expose his criminal activities.
Venning woos Lynne, much to the envy of Sam, before telling her that he is going to Amsterdam on business. In reality, he is arranging for the next shipment of diamonds to be smuggled into the UK.
She asks if she can accompany him and he refuses, but invites her to move into his lavish Chelsea pad.
Lynne tips off Willoughby who is becoming increasingly concerned for her safety and puts one of his men on her tail. It proves to be a wise move since Venning’s hired killer, Hewson (Brandon Brady), discovers that Lynne is the sister of the undercover policeman they murdered.
Lynne is kidnapped and held on Venning’s boat as he plans to skip the country and kill her once they are safely out of the way.
Det. Insp. Willoughby
Det. Sgt. Robbie Roberts