A reporter enters a restaurant to interview Laura Quinn, the only woman to ever have been a manager at the London Diamond Corporation, for a puff piece about the first generation of women entering the workforce. Quinn places a box on the table, revealing a huge diamond, and says, "I stole it." The reporter, suddenly enthralled, assumes that Quinn has been in prison for the theft all this time. The story then flashes back to 1960, when Quinn was still employed as a manager at London Diamond Corporation. She is passed over for a promotion for the sixth time despite being intellectually superior to her male co-workers. Quinn discovers that she is getting fired from the janitor, Mr. Hobbs. He offers her a place in a plot: stealing enough diamonds to make them rich, but not enough to be noticed. Knowing she is considered old by her coworkers and has few other professional prospects, she agrees. At a social event at the Company President's mansion she finds the vault combination codes. Quinn and Mr. Hobbs hatch a plan, exploiting a weakness in the new camera security system. However, Mr. Hobbs steals every single diamond from the vault, almost two tons worth, and holds them for a ransom of 100 million pounds. The head of the insurance syndicate from King's Row is forced to pay the ransom, leaving him financially ruined. Quinn, having never agreed to this, now finds herself trapped. The company hires a private investigator, Mr. Finch, to keep the matter from going public. Suspicious from the start, Mr. Finch keeps a close eye on Mr. Hobbs and Miss Quinn. Quinn wants to avoid jail time by giving the diamonds back but Mr. Hobbs refuses. Having no idea where he's hidden them she conceals their scheme.