When a probe from an unknown alien source unleashes a devastating assault upon Earth, Enterprise is recalled, then sent to search for the perpetrators in a mysterious region of space known as the Delphic Expanse.

John Fleck (Silik)
Vaughn Armstrong (Admiral Maxwell Forrest)
Gary Graham (Ambassador Soval)
Daniel Riordan (Captain Duras)
James Horan (Humanoid Figure)
Bruce Wright (Dr. Fer'at)

Dan Desmond (Klingon Chancellor)
Josh Cruze (Captain Ramirez)
David Figlioli (Klingon Crewman)
L. Sidney (Klingon Crewman #2)
Gary Bullock (Klingon Council Member)

• The Vulcan ship Vaankara was destroyed in the Expanse. The last video transmission shows the crew had gone insane and killed each other before the ship was destroyed. The Vulcan High Command recalls T'Pol to Vulcan. She resigns her commision to stay aboard Enterprise.
  
• Trip's younger sister, Elizabeth, is among the 7 million people killed in the Xindi attack.
  
• This is the final appearance of the Humanoid Figure (a/k/a "Future Guy"), who informs Archer that the Xindi are responsible for the attack. An enemy faction supplied the Xindi with information that Earth was responsible for the future destruction of the Xindi homeworld.
  
• Ramirez is captain of the Starship Intrepid, one of the vessels that comes to Enterprise's aid when under attack by Duras.
  
• A second Warp 5 starship, NX-02, is under construction in orbit around Earth. It will be ready to launch in 14 months.
  
• Enterprise gets an upgrade, adding photonic torpedoes and enhanced hull plating, along with a new command center. With the new weapons, they are able to destroy Duras' ship before entering the Expanse. They also added a group of military soldiers (who won't be seen until next season premiere).