“The Great Leap Forward” is episode thirteen of season four of The 4400 and the season and series finale.
In the previous episode, “Tiny Machines”, Diana shot RossTom. She and Doyle get him to Shawn to heal, but first Marco needs to inject him with the polonium to erase Ross. Meanwhile, Danny arrives at the hospital with his mother, who was bleeding from her eyes and nose. A paramedic comes over to tell him to expect the worst; this is a textbook case of promicin fatality. Danny says his mother didn’t take the shot. Then the paramedic starts bleeding and collapses.
Shawn is working to revive Tom, who has flatlined, but he says it’s too late. Then Tom revives, his bullet wounds gone. He tells Diana he thinks he killed people. Doyle tells him to rest; they’ll talk later.
Danny is inside the hospital, talking about the paramedic, when a nurse comes over wanting his mother’s details. Then she starts bleeding and collapses, as do yet more people in the hospital. Danny runs out the doors.
Tom punches the mirror, because he remembers things he did when he wasn’t himself, all bad. Doyle treats his hand and he asks her how positive she is the thing is gone. She tells him they’re going to watch Tom to make sure. And, when he recovers, he can tell them who the Marked are.
Abigail is telling Garrity, Marco, Diana and Brady that the hospital is quarantined. Garrity spoke to a doctor; there have been dozens of deaths. There’s no way everyone took promicin and it’s spreading too fast to be injected. Marco suggests someone took promicin and their ability is spreading it like the flu. Abigail says that for every person who died, someone will have survived with a brand-new ability.
Shawn is watching the news when Joanna tells him Danny wants to see him. And he’s waiting outside in the gardens, refusing to come in or let anyone near him. Danny tells Shawn that he took the shot and the people at the hospital are because of him. He thinks he’s infecting people with promicin and can’t turn himself in without making people sick. Shawn doubts Danny can infect those who are already positive, so he will keep them away from Danny until Burkhoff can give Danny some inhibitor. They can figure it out. Danny tells Shawn their mother is dead.
Isabelle heads to see the captive Jordan Collier. She wanted to tell him something before he changes; she did want to change when Kyle brought her to Promise City. But she isn’t meant to lead a normal life. Collier tells her she still has a choice; she doesn’t believe it. He also asks her to kill him, but Parrish comes in. Outside. Parrish tells Isabelle they won’t let Richard go yet. And demonstrates the kill switch they installed in Isabelle when she says she will go get her father herself.
Kyle is holding a press conference, telling everyone that they had nothing to do with the deaths, and Jordan Collier is missing, but the P+ are offering their services to the authorities to help. The conference is being watched at NTAC when Garrity and another agent return; it looks like what happened at the hospital has stopped. Then a reporter outside the hospital starts bleeding. Followed by the woman who came back with Garrity. Then more start collapsing, including Brady.
Afterwards, it seems the sickness is spreading. The police and emergency services were hit first and the army has quarantined Seattle. Diana asks Marco what the promicin test showed. Everyone who survived is positive. Except for Diana. Marco thinks Burkhoff experimenting on her with an early type of promicin helped her body develop a resistance.
Danny has been given the inhibitor and Shawn talks to Burkhoff. He doesn’t really want to hand him over to NTAC, because Danny might never be seen again, but that might be the only way to develop an antidote.
Diana is now at Tom’s with Doyle thinks they need to take Kyle up on his offer. The government is focusing on containment. She’s going to go to Promise City, but wants Diana to head to the 4400 Centre to see if Burkhoff can figure out why Diana is immune. Tom hears about his sister. He needs to go get Collier, as Tom knows where he’s being kept and the other Marked still think Tom is one of them.
Doyle meets with Kyle; it seems Collier already had a plan in place for taking control of the city. Parrish is talking to someone, saying this is a chance to declare war on the Positives, then tells Isabelle she needs to kill Kyle, when Tom arrives as Isabelle is leaving.
The situation has now changed a lot, though there are going to be a whole bunch of new issues to deal with. Unfortunately, the series wasn’t reviewed for another season, so there are a whole bunch of threads left dangling and no real resolution to most of it, only different problems.