Something's off between Myka and Pete since she came back. She tries to talk to him about it, but he has nothing to say. Mid-conversation, they're called to investigate the illness of two men who seem to be rapidly regressing to childhood, and maybe even past it. Since both men were scheduled to testify in a murder trial, Pete goes to speak to the accused and his lawyer, but only gets a barrage of questions.
Artie sends Claudia and Jinks to an auction to buy the knife of Typhoid Mary, an artifact that can pass any illness from one person to another. Claudia is thrilled at her first official mission, but Jinks is deflated at the thought of a boring auction compared to last week's derring-do. They win the knife, but when they go to collect it, they find out it was stolen! They track down the culprit, but he gets away with the knife!
Perhaps more upsetting to Claudia is her discovery that Artie has been surveying her mission. She is crushed when she thinks he didn't trust her, but when she finds out that he just wanted to see her in action, she regains the stamina to find the knife and the thief.
Claudia and Jinks find the thief standing by a young man in a hospital bed, where he explains that he couldn't let his son, who has a family of his own, die of leukemia. He used the knife to take the cancer from his son so that he could live a normal life. The agents bag the knife, but allow the kindhearted man to stay with his now healthy son. Jinks's worries that the job would be dull have all been washed away.
Pete is not faring so well: He has been struck by the same regressive disease as the two men they're investigating, as has a pugnacious reporter. After studying footage of the reporter interviewing the lawyer, Myka notices an out-of-place tie clip on the latter. Following up with him, she discovers it belonged to Walter Winchell, a journalist known for his grueling interrogation rounds. The connection becomes clear: anyone who was questioned by the lawyer - the witnesses, Pete - regresses to a state of childhood. The clip, along with a matching set of cufflinks, was inherited by Sarah Bell, mother of Eric, one of the victims - who recently made a miraculous recovery.
Myka rushes to the Bell residence and demands the cufflinks, which restore memories to the victims, but Sarah refuses, holding the cufflinks above the garbage disposal. Eric, seeing Myka with a gun pointed at his mother, decides to end the charade: he was guilty of the murder, and admits it. His mother, trying to protect him and send his innocent friend to prison in his place, used the clip to wash memories from the minds of witnesses, and used the links to restore her son. Myka secures the links and heals the remaining victims.
That done, Myka meets with the regents to convince them she's 100% able to be back on the job. With their preternatural intelligence, they see that she is ready, and reinstate her as a full agent.
Pete and Myka get sucked into a 1940s detective noir novel in search of an artifact. Meanwhile, Artie, Steve and Claudia chase down a phantom car thief.
Get a laugh with the best lines of Warehouse 13 Season 4, Episode 17.