In and of itself, "Reciprocity" is an average episode in line with those of the first season. But this is the third season of Fringe, which has become more serialized over time, and everything that happens has an implication for the future. With this in mind, "Reciprocity" becomes a fairly exciting episode as shapeshifters start dying.
The final revelation that Peter is the killer is really awesome, enhanced by Walter's suggestion that the machine somehow changed Peter. While we don't know exactly what's going on, Peter is different, changed by the machine or extra angry from the Fauxlivia fallout.
Score: 9.0/10
