A Fringe investigation is triggered when a patient at a mental institution undergoes an impromptu brain surgery that unexpectedly leaves his brain exposed. Despite the unthinkable circumstances, the patient's condition and sanity miraculously improves before the Fringe team arrives. While Agent Dunham and Peter scan surveillance tapes (and Walter enjoys his pudding), Olivia recognizes a familiar face as Thomas Jerome Newton (guest star Sebastian Roche), the leader of the shape-shifters. As similar cases stack up, the Fringe team heads back to the lab to determine exactly how patients are being cured. Walter's brains are put to the test and William Bell (guest star Leonard Nimoy) resurfaces.