Earth is savagely attacked by a mysterious alien probe that leaves millions of people killed. When Archer learns that the culprit species is planning to destroy the entire planet with their next assault, Enterprise embarks on a new mission into the dangerous and highly mysterious Delphic Expanse to put a stop to it. Although T'Pol is given a direct order from the Vulcan High Command not to participate in this mission, she resigns her post in order to continue with Enterprise. Meanwhile, the Klingons, who are bent on destroying Archer, continue their hot pursuit of Enterprise all the way into the expanse.
