In the 2020s a Romulan time traveller named Sera tried to kill the young Khan Noonien Singh in Toronto, and La'an Noonien-Singh stopped her.
Sera, a disguised Romulan from the future, worked in Toronto to change history so that the Federation would never form. A wounded temporal agent drew La'an Noonien-Singh into the altered timeline, where she found a United Earth Enterprise commanded by an alternate James Kirk, and the two travelled to Toronto to set history right.
Kirk was killed by Sera during the mission. When Sera tried to assassinate the boy Khan at a genetics institute, La'an killed her and chose not to harm the child, and the timeline was restored.