A young Etta is playing in a field as Olivia and Peter look on. As people start to run, Peter gestures to his daughter and then sees an explosion in the city. Observers walk across the field as Olivia and Peter run to Etta. Peter suddenly finds himself in an ambulance demand to know where Etta is as EMTs tend to Olivia...
Peter wakes up from his nightmare and looks around. Walter is sleeping on a couch nearby and Peter goes to the next room to check on Etta. She's fine and asks if he's all right, and he assures her that he was just checking on her. Once she leaves, Etta looks at the necklace of a bullet around her neck.
Walter wakes up and notices light flashing on the wall. He gets up and checks, but is unable to see the source across the street.
Peter checks on Astrid, who is in the next room playing Scrabble on the computer and drinking coffee. Walter comes in and says that they need to find Olivia, and gives them the address in New York City where Olivia called him 21 years ago. He tells the others that Olivia had a crucial piece of the equipment that he worked with in conjunction with September. After they completed each piece of equipment, September scrambled the knowledge in Walter's mind. September then told Walter to retrieve something from Grand Central Station that would make everything okay. Walter sent Olivia there and she disappeared, and he had them ambered a few days later. As Walter goes to get dressed, Peter assures Etta that if Olivia is alive then they'll find her.
The team takes to the streets and drives to the address where Olivia disappeared. The Observers have paved over the nearby park and built a machine to pump carbon dioxide into the air to suit them. The machine is one of several built around the world. There is a nearby city-block sized piece of amber and Walter figures that Olivia may have used amber as a last resort to avoid the Observers. They go over and discover person-sized holes cut in the amber, and Etta explains that amber gypsies took some of the people embedded inside.
That night, the team goes to an outdoor black market. Etta warns that they know her and sends Peter and Astrid on with a handful of walnut, now a precious commodity. They talk to the amber gypsies and ask to see their "stock," and the gypsies send them on. However, once they go to the display area, one of the gypsies triggers a hidden alarm.
While they wait, Walter talks about remembering Etta as a child, which was just a few months ago for him since he was frozen in amber. Touched, Etta kisses him on the cheek.
Peter and Astrid look over the various individuals sealed in extracted pieces of amber. When they don't find Olivia, Peter goes back and asks the head gypsy if he's seen someone matching Olivia's description with an electronic device in his hand. He finally offers the walnuts and the gypsy confirms that Olivia was sold.
Edward Markham is at home watching television and using the amber block containing Olivia as a table. The doorbell rings and Markham immediately yells that his apartment is sanctioned. Peter calls to him and Markham insists that Markham died saving a school bus. Peter bursts in and disarms Markham, who wonders where he's been and why he didn't age. They spot the block of amber and Markham insists that he loved her ever since Olivia first came into his bookstore. He explains that she's supposed to wake up and see him as his savior. Astrid finds a gurney and they start hauling the amber out while Markham insists that he's gone into debt to save Olivia. Etta goes to the block and looks in at her mother.
The amber gypsy reports level four information to the hotline loyaltist line.
Etta checks to make sure the way out is clear while Peter loads the amber block into their van. Walter admires Markham's collection of rare books just as an Observer comes in and draws a gun on him. Etta shoots him and tells Walter to run as another Observer teleports in and stuns her. When Markham begs the Observer not to kill him, Etta recovers enough to shoot the second Observer. She runs down to the van but she and Pete realize that Walter hasn't made it. They're forced to drive away as loyaltist policemen arrive and capture Walter.
Back at the lab, the team softens the amber for the split second to free Olivia and Peter explains that she's in the year 2036. She explains that she ambered herself and then sees Etta. Peter tells Olivia that their daughter found them and introduces Etta to her mother. Etta goes to Olivia, who stares in shock and then says that she's beautiful. They hug and then Olivia asks where Walter is, and Peter tells her what happened. Olivia shows them the electronic device that Walter sent her to recover and Peter says that they're working on finding Walter.
Walter is strapped to a chair in a small interrogation room and Inspector Windmark comes in to see him. Windmark says that he doesn't know how Walter is alive and tries to read his mind, only to discover Walter trying to block him by thinking him of music. The Observer says that they tolerate music but it means nothing to them. Walter insists that it amazes him and helps him shift perspective and see things like hope. Windmark tells him that there is no hope for him and says that it's his choice whether Walter ends up as a human or a vegetable.
Etta takes Peter, Olivia, and Astrid to an underground hideout and calls to her conspirator, Anil. Anil and another Fringe agent, Klopinski, are there sharing a toast to a dead comrade, Elias. Etta toasts her friend as well and then asks Alin for help.
As they wait, Olivia looks out across the Observer-dominated city and realizes that they failed to save the world. Peter agrees but says that Etta has been trying. He admits that he never thought he'd see her again and Olivia starts crying as he talks about how he left her alone when she went to New York and he stayed in Boston to search for Etta because he didn't have Olivia's strength. Olivia points out that they were both suffering from the loss of their child but Peter explains that he didn't care about anything else except finding Etta.
Etta calls them in and Anil explains that the device Olivia recovered is a transilience thought unifier, model 11, and it accesses the wearer's hidden thought. He admits that it doesn't work any longer and Peter figures that they can use it to recover the information of the Observer device from Walter's mind. They pick up Walter on the security cameras, being taken to Observer headquarters. Peter warns that the Observers could take the information from Walter's mind.
Windmark probes Walters' mind, demanding to know who freed him and why. Walter continues resisting and Windmark realizes that his mind is deliberately partitioned to protect something valuable. He wonders if an Observer did it since no one else would know the technique, and tells Walter to put the pieces together for him. Windmark begins to pick up parts of what Walter is thinking and applies more telepathic pressure as Walter convulses. He's surprised that Walter can fight back and admits that if he had a unifier he could put the thoughts together. It will take too long but the Observer assures Walter that he will still succeed without it. He continues probing and gets flashes of Etta as a young girl, and wonders how a small child can help him. Walter refuges to give up her name and finally passes out.
As Etta checks the city-wide monitors trying to find Walter, Olivia tells Peter that their daughter is amazing and Peter admits that seeing Etta is a dream within the nightmare. Etta finds footage of Walter being taken into the Napean Building and Alin says that they've been working on tech. Klopinski warns that it isn't perfected but Alin explains that the tech will make a human appear dead. However, if they use it then it will reveal its existence to the Observers. Etta insists that Walter's plan will save them all and Alin and Klopinski agree.
A short time later, Amber drives up to the Napean Building and tells the loyaltist tatties that Windmark wanted the bodies of the resistance fighters brought to him as soon as possible. Once they unload two body bags, the loyalist officers scan Elias and Peter's bodies and confirm that they're dead. As their leader goes in, he tells Etta that he was recently promoted to Level 6 and tells Etta that they found her superior, Foster, embedded in Amber. He doesn't know what they did with him and suggests that Etta asks Windmark, who will want to talk to her about it.
Windmark points out that the physics in Walter's are above his level of comprehension and probes to find out what the stones that he sees in Walter's mind can do to defeat them. The Observer insists that he's Walter's ally and tells him to lower the walls.
Etta wheels the corpses into a storage room as a tattie loyaltist starts to strip them for valuables. She shoots him and then revives Peter. They slip into Observer headquarters and open the outside door, letting Olivia in. The trio goes to the temporary atmospheric converter in the building and Peter sabotages it.
Windmark tells Walter that they are done just as the air control malfunctions. The inspector leaves and Peter and Etta break in and free the comatose Walter. They take him out, shooting down any Observers and tatties in their way. They rendezvous with Olivia and head for the van, Olivia providing cover fire. Astrid is waiting and they drive off through the barricades. Walter asks Astrid for some music before passing out.
After the shootout, Windmark scans the security footage and realizes that Etta is the girl that he saw in Walter's mind.
Back at Etta's apartment, Walter wakes up and tells Olivia that he's glad to see her alive. When Peter gives her the unifier, it activates on its own and they realize that it's keyed to Walter. However, Walter no longer remembers the plan that September told him due to the mental damage that Windmark inflicted on him. Sobbing, Walter tells them that he can't do it and walks away, and Olivia realizes that all the parts are gone from Walter's mind and there's nothing to unify. Etta figures that they were destroyed when Walter fought the Observer's mind probe and that the plan is gone.
Later, Walter is trying to sleep when he notices the same refracted light that he saw earlier. He goes out and discovers that the reflection is coming from a mobile made of old CDs. He finds a bag of the Ds nearby and goes through them, finding one that will pay on the D player of an abandoned taxi. Walter sees a single dandelion growing through the sidewalk and smiles.