In a U.S. Army research meeting, taking place in 1985, Walter brings out a digital cell phone from the alternative universe. William and Bell developed a window, which is able to catches photons and images from the other side.
In our time, Walter goes to visit Olivia to explain about Peter.
He shows Olivia the window to the other universe. He explains that after Peter became sick, nothing else mattered anymore. The illness was genetic, and the old hope was on the Other Side because they are more advanced technologically.
Back in 1985, Walter watches himself through the window conducting experiments to save Peter. He gets a call from his wife to go home. A young Peter gives his father his lucky silver dollar, and then dies in his arms.
After his funeral, Walter shows his wife the window and Peter alive in the other universe. He showed her this to her to help her move on, knowing that there is another Peter somewhere that will grow up and have a full life.
Walter then spies his other self come up with the cure, but an Observer suddenly distracts him from his work. The cure is lost…
The Observer explains to others like him that a mistake was made. This could alter the future; create a new set of probabilities. This mistake and Peter are significant to the Observers.
Walter explains that he now must create a cure for the other Peter, because the other Walter was distracted by a man (Observer). Walter must create a wormhole, to bring the cure to Peter.
Walter heads to Reiden Lake with the transportation device. Nina and Dr. Warren arrive at the lake to try and stop him. They are unsuccessful, and Walter crosses to the Other Side and the vile in his pocket breaks.
On the Other Side, Peter gives his mother Elizabeth his lucky silver dollar in case he dies. Our Walter arrives and convinces her to let him take Peter to the lab without her. He then takes Peter through the transportation device, back to our world.
They immediately fall through the ice into a frozen lake. The Observer jumps into the lake and saves them. He explains to Walter that Peter is important and cannot die.
Walter saves Peter with the antidote, and then his wife arrives and sees her son, now alive.
Walter then explains to Olivia, that despite what he promised he fully intended to keep Peter.