After killing Maureen the matron, Libby has moved into her flat, bringing the kidnapped baby Anna. Bitsy reveals to Sara that Libby has black teeth. She also tells Sara where she can find a photo of Libby, which Lucius steals from the hospital.  Markoe is concerned about what Sara might do with her knowledge of the "Research Wing." Lucius tells Sara the matron was absent from work. Sara and Lucius break into her apartment and find Maureen dead. Libby is ingesting poison and passing it on to Anna through nursing, without the neutralizing agent. Kreizler diagnoses Libby as unravelling. Colleen finds Libby in a mugbook. John plans to put Libby's photo in The TImes and Libby finds out. Libby was an associate of gangsters. Cyrus recognizes Libby, who used to be Goo-Goo Knox's girlfriend. Libby breaks into Sara's office and steals her father's gun, leaving a warning. Sara moves in temporarily with John. Laszlo invites out Karen Stratton for dinner. He asks for advice on the case. Sara ignores John's request and goes hunting for Knox. Joanna offers to help Sara. They find Libby with Knox at a dogfight. They follow and watch them having sex. Sara trails Libby and sends Joanna to fetch help. She interrupts John's evening out with Violet, who gets miffed. Libby is staying at Knox's abandoned boardinghouse. Byrnes suggests Hearst go after Sara in The Journal. Sara breaks in through the cellar. John arrives and follows Sara's path. Kreizler gets accosted by a duster, Fat Jack. Marcus comes to his rescue. Libby, armed with a gun, sneaks up behind Sara. Sara throws ash in her eyes. But Libby escapes when Sara chooses to rescue Anna. John, then the rest of the team, finally arrive. They return Anna to the Linareses. John and Sara make love.