Working together to find a way back to their respective timelines, the Starfleet officers and Legionnaires have split into two teams, with members of both groups on each team. One group travels back in time to the moment when their own histories were truncated and this new blended timeline came into being, while the other team travels to the heart of the Imperial Planets of Earth. So as one team finds themselves witnessing what happened in the deep past to change history, the other team discovers the far reaching effects of the aftermath in the present.