A surprisingly serene Walter tells Peter they can find September. The memory the Observer child, Michael, showed him is in his subconscious, so Walter can use the sensory deprivation tank. He enters the memory and pinpoints Donald's apartment in Brooklyn, and Walter, Peter, Olivia and Michael go there.
Outside, Peter asks Walter why he's now so cheerful, and Walter says Michael's touch gave him a new perspective, as well as restoring memories from the other timeline - although he still doesn't remember the plan.
Captain Windmark travels to the future and reports to the Commander that Anomaly XB-6783746 was hidden in 2036, because someone thought it was important.
September answers the door, amazed to see the team. He kneels down to look at Michael and they hold up their palms, facing outward, and touch.
September explains he was apprehended before the invasion and punished for repeatedly interfering with the timeline and interacting with the Fringe team. The Observers removed his chip and exiled him to this era. Now he's just a regular human. He named himself Donald O'Connor because the first movie he watched with Walter was "Singin' in the Rain."
September explains that Michael was born hundreds of years from now. Like all of their kind, he was created in a lab with the genetic material of a designated donor. On February 20, 2167, a scientist in Oslo, Norway, rewired the portion of the human brain that induces jealousy and increased cognitive function - sacrificing emotion for intelligence. This was the catalyst for the Observers' creation. Eventually, humanity stopped valuing emotions, and even the positive ones were machined out.
Early in the boy's maturation, scientists realized his brain had developed differently. To them, he was a defect. September had observed in the Fringe team's time how fathers cared for their sons and protected them. It stirred something in him that he could not ignore. He hid the boy in the past, where he would be safe.
Walter asks, he's your son? Yes.
Windmark has also learned about the boy's origin. He asks the Commander for a protocol suspension to travel back to a moment when he can eradicate the fugitives, who possess the anomaly. The Commander says no, they are inconsequential, and the anomaly poses minimal risk.
September says that moment when scientists first decided to sacrifice emotion to increase intelligence was the turning point in human evolution. If they send the boy into the future, to that moment, he can demonstrate a different kind of intelligence, an enlightenment that goes beyond knowledge or cognition. Then those scientists will never follow that path, meaning the Observers will never exist. This was the plan. But September devised it after his chip was removed, so he needed Walter's help.
The materials the team has been gathering are for a device they must build. It also requires tech from September's time, which he took from the future long ago and hid nearby.
Because September is a known offender, he has a tracking chip. But Donald's apartment is unoccupied when Windmark and his minions arrive. An Observer finds bloody tweezers and thinks September removed his chip, but he doesn't see it.
In the van with the team, September has a device that shows the Observers are in his home. He remotely detonates a light bomb to destroy it, but the Observers teleport away.
While retrieving the tech from September's storage space, Walter tells him what Michael did. He says that, when September pulled him and Peter from Reiden Lake and said, "The boy is important; he must live," he was talking about Michael, right? Yes. Walter reveals that Michael also showed him something he hasn't shared: For the plan to work, Walter must sacrifice himself.
September has to get a few more things they need. He touches his son's hand, promising he will see him again, and leaves.
But the streets are roadblocked. The team stashes the van and, back at Harvard, Astrid determines they can escape on the monorail. Loyalists swarm the platform, but Olivia and Michael get onto the train. The Bishops get into a different train car.
As the doors to Michael and Olivia's car close, Michael steps off the train, right in front of the troops! The train departs, and the Loyalists deliver the boy to Windmark. He leans down and says, "Hello."