“Reciprocity” is episode eleven of season three of Fringe.
Broyles, Olivia, Peter and Walter arrive at the hangar where all the parts of the machine that was discovered in “6955 kHz” are being stored. Nina Sharp is being briefed about how they aren’t making progress. She meets the others; she understands the encryption on the laptop has been broken. Peter had several password suggestions. Walter says Fauxlivia – his name for AltLiv – has ruined U2 for the rest of them. Walter is gazing at the machine, which has been assembled.
Dr James Falcon, the lead scientist, says they don’t know how it works. Several of the people working there start noticing an odd electromagnetic spike. Nina is saying to the others that the problem might be the piece Fauxlivia stole. Then they hear noises behind them as the machine starts doing something. Peter is bleeding from the nose. When it’s commented that it looks like something triggered the machine, Peter says something did. Him.
Peter enters the house at night quietly and is making a snack when Walter comes in. Walter asks if he’s been out. Peter says he hasn’t. Lying, for some reason. They talk, including about the First People book. Walter has found nothing in it about how the machine works or how it’s connected to Peter.
Peter is going to be tested at Massive Dynamic to see if they can work out why he had an effect on the machine. Walter is worried. He speaks to Nina in private; though he’s terrified about this, he wants her to do a favour for him. He’s been trying to regenerate his brain cells but William was too clever for that and inhibited his brain’s ability to replicate. But William will have kept detailed notes; if he can see the research, he will know how to reverse the effect. He has to get smarter to help Peter. Olivia has joined Peter in the other room; she tried calling him last night. Peter says he went for a walk.
At the Massachusetts Port Authority, a man sees dead fish in the fountain. He investigates, and finds a dead body as well.
Broyles finds Astrid at the lab and talks about the file on Fauxlivia’s laptop. She’s happy to help. Broyles explains that many of the references deal with Peter. He gives her the details, then gets a call. Walter, Falcon and Olivia are observing Peter, whose heartrate is elevated unusually during the test. Walter is worried. Olivia gets a call.
Olivia and Broyles are at the Port Authority. The dead man worked there. The fish are dead from mercury poisoning, because he was a shapeshifter. His data storage disc has been removed. They wonder why he was killed; Olivia suggests Walternate is tying up loose ends before they learn what the shapeshifters know. Broyles calls Astrid; she confirms the dead man’s name is in the file. Broyles tells her to shut down access; no-one but her gets to see the file. If Walternate knows they have the file, someone on their side must have told him. They have got a mole.
Peter has finished the test and Falcon tells him that, apart from the elevated heartrate, they found nothing. Walter comes in and explains about the shapeshifter and how someone on the inside is feeding Walternate info. Falcon is eavesdropping.
They are discussing the matter in the lab; Astrid is checking all the names in the file. Olivia offers to sift through the data. She’s told that’s probably not a good idea. Peter realises that Fauxlivia will have written about him.
They head to Massive Dynamic where everyone is being tested with a lie detector William Bell designed. Peter wants to keep everyone in custody until they know who it is. Nina wants a word with Walter. She found William’s research; he designed something to regrow Walter’s brain tissue. However, there were three samples for different animals and the labels were destroyed. They need to check them first. Walter sniffs the first anyway.
There are several shapeshifters in Fauxlivia’s file, and whoever is hunting them down seems to know who they are. Which means they need to uncover the identities of those left quickly.