Aboard Degra's ship, Archer, Reed and Hoshi work with the Arboreals and Primates to stop the Xindi weapon from launching. Archer plans to destroy the weapon from the inside by overloading the power systems, but he needs Hoshi, who is still recovering from her ordeal with the Reptilians, to decrypt the weapon schematics. Meanwhile, T'Pol leads Enterprise to Sphere 41.

Scott Bakula (Captain Jonathan Archer)
Jolene Blalock (Commander T'Pol)
John Billingsley (Doctor Phlox)
Linda Park (Ensign Hoshi Sato)
Anthony Montgomery (Ensign Travis Mayweather)
Dominic Keating (Lieutenant Malcolm Reed)
Connor Trinneer (Commander Charles 'Trip' Tucker III)

Scott MacDonald (Xindi-Reptilian Commander Dolim)
Rick Worthy (Xindi-Arboreal Janaar)
Tucker Smallwood (Xindi-Primate)
Josette DiCarlo (Sphere-Builder Woman)
Bruce Thomas (Xindi-Reptilian Soldier)
Andrew Borba (Xindi-Reptilian Lieutenant)
Matt Winston (Daniels)
Mary Mara (Sphere-Builder Presage)
Ruth Williamson (Sphere-Builder Primary)
Jeffrey Combs (Commander Shran)

Gunter Ziegler (Doctor)
J. Paul Boehmer (Officer)
Zachary Krebs (Andorian)

• Season 3 Finale, and the end of the Xindi story arc.
  
• Enterprise destroys Sphere 41, which in turn destroys each of the other spheres and the Delphic Expanse begins to return to normal space.
  
• Shran arrives in time to help destroy the Xindi-Reptilian ship.
  
• T'Pol tells Trip that she is not old; she is only 65 years old.
  
• Daniels shows Archer a ceremony that is the beginning of what will become the United Federation of Planets. This will be seen in the series finale "These Are The Voyages...".
  
• Archer appears to have been killed when the weapon is destroyed. When Enterprise reaches Earth, they can not raise anyone on comm and the shuttlepod is attacked by WWII aircraft. In the final scene, Archer is seen unconscious in a Nazi medical camp and an alien in Nazi uniform emerges from the shadow.
  
• This episode was nominated for an Emmy award for Outstanding Prosthetic Makeup.