Stardate 1581.2: A man suddenly appears on the Enterprise as La'an Noonien-Singh is walking down a corridor. He has a gunshot wound. Before he dies, he speaks of an attack in the past, gives her a device and tells her to go to the bridge. On the bridge, La'an notices that reality has changed. Instead of Pike, James Kirk is in command of the Enterprise, which is a ship of the United Earth Fleet. The Federation doesn't exist. I the ready room, as Kirk and La'an wrangle for the device, it activates and transfers them to 21st century Toronto. They have no idea what to look for and how to find out without any modern technology. When the recently built Lake Ontario Bridge gets destroyed by a bomb, they both remember that it happened in their respective timeline. So whatever triggered the change is still about to happen. They witness how a piece of debris with evidence of a photonic bomb is loaded into a van. Kirk steals a car and they follow the van, but they get stopped by the police. A woman named Sera, who was already present at the site of the bombing, talks the police into releasing the alleged "civil rights lawyer". She tells La'an and Kirk of a big international conspiracy and of a cold fusion reactor in Toronto. Kirk knows that in his timeline the city would be destroyed by the Romulans, apparently by targeting that reactor. But there is no equipment to locate it. La'an remembers that Pelia spoke of a site in Vermont where the future engineer used to live. The three come up with a method to detect tritium as used in the reactor using the phosphor coating of an old diver's watch. Back in Toronto, Kirk and La'an find the entrance to the reactor. La'an can get access because of her DNA. It is the Noonien-Singh Institute. But Sera has been following them. She is actually a Romulan temporal agent, whose mission is to stop human progress. She kills Kirk and forces La'an to walk in with her. But instead of blowing up the reactor, she heads for the genetic engineering section and a door labeled "Khan". La'an manages to kick the gun off her hand and finally shoot Sera, who vanishes. She then tells Khan, still a boy, that no one will hurt him. Back on the Enterprise, an agent of Temporal Invesigations from the future appears and tells La'an never to speak with anyone about the incident.

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