Susan Marlowe, librarian and retired jewel thief, gets involved in her old life when her fiancé, Richard Scott, an insurance investigator, asks her if she can discover the identity of the person who fashioned the replica of a stolen pink diamond. Susan’s investigations get her into a confrontation with a murderer and into collaboration with The Phantom, a charming and notorious high-end thief.Soon Susan and The Phantom are working together to entrap the killer, who is seeking revenge against The Phantom for a past wrong. When an elaborate scam that they hope will ensnare the killer doesn’t go as planned, Susan finds herself in the library facing an enraged murderer where she must rely on her own quick wits and luck to survive.