La'An is pulled into an altered timeline and travels to 21st-century Toronto with that timeline's Captain Kirk to stop a Romulan from killing the young Khan.
A dying stranger hands La'An a time-travel device, and she finds herself in an altered, war-torn timeline where James T. Kirk commands the Enterprise. The two travel to 2020s Toronto to find the point where history diverged, and a romance grows between them.
The trail leads to a lab where a young Khan Noonien-Singh is being raised. A Romulan time traveler, Sera, intends to kill Khan to prevent the Eugenics Wars and, with them, the founding of the Federation. Sera kills Kirk, and La'An kills Sera and lets Khan live. Back in her own timeline, a temporal agent swears her to secrecy, and the Kirk she meets does not know her.