St. Claire, present day: The new villain named Newton suprevises brain surgery over a crazy man. The results: remarkable. The man is sane again.
St. Claire, several years ago: Dr. Walter Bishop is about to go under Dr. Paris's scalpel. The results: remarkable. Brain tissue is removed wich in fact is what made him go insane.
Only catch is that Dr. Paris is none other than William Bell and the brain tissue he and Nina Sharp removed exactly what Newton and his men are trying to put back on Walter's head. Confronted by the choice to either stop them or help Walter, Olivia releases Newton in exchange for the exact dosage of the antidote that would save Walter's life before a neurotoxin would kill him right in Peter's arms.
As emotional as Olivia's reaction my have been this episode is in fact an exercise on the emotions of father and son, from the way that every image reminds Walter of Peter to Peter's despair once his father is dying and both of Bishops tini glimpses into how they really feel about notoriously absent Mrs. Bishop.
Peter's relief over Walter's welfare is palpable and while there's no doubt in my mind that the father he sees in him will be gone the minute he finds out the truth, this childhish remain of what was once brilliant Dr. Bishop is the man Peter calls his family, a man who needs him for his very survival and genuinely cares about him despite he isn't the son he lost.