Six weeks into the Delphic Expanse, Captain Archer and his crew are still searching for clues regarding the mysterious Xindi. They're also adjusting to the newest members of the crew, a squad of Military Assault Command Operation soldiers (MACOs), led by Major Hayes. The crew learns of a Xindi working at a mining complex, and set out to track him down.

Scott Bakula (Captain Jonathan Archer)
Jolene Blalock (Sub-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)

Richard Lineback (Kessick)
Stephen McHattie (Alien Foreman)
Tucker Smallwood (Xindi-Primate)
Randy Oglesby (Degra)
Rick Worthy (Xindi-Arboreal Janaar)
Scott MacDonald (Xindi-Reptilian Commander Dolim)
Marco Sanchez (Corporal Romero)
Daniel Dae Kim (Corporal Chang)
Nathan Anderson (Sergeant Kemper)
Steven Culp (Major Hayes)

Chris Freeman (Alien Head Guard)
Adam Taylor Gordon (Young Trip Tucker)
Erin Price (Elizabeth Tucker)

• This is the first time a story line has spanned an entire season in a Star Trek series.
  
• The facility is mining Trellium ore, which is used as insulation on starships in the Expanse.
  
• This is the first appearance of the Xindi council. We see that there are five sentient Xindi species: Primates, Arboreals, Reptiles, Insetoids, and Aquatics. The Insectoids and Aquatics are CGI characters.
  
• Tarik Ergin played the Insectoid during filming and was replaced with CGI during post production. (He previously played the background character Ayala on Star Trek: Voyager.)
  
• One of the storage bays has been converted into a new command center.
  
• Since she resigned her commision, T'Pol now wears new bright jumpsuits instead of her Vulcan uniform.
  
• Phlox requests that T'Pol begin Vulcan neuropressure treatments with Tucker, who is having trouble sleeping since his sister died.
  
• Kessik is fatally wounded during the escape, but he is able to give Phlox a set of coordinates. When Enterprise arrives, they find the planet has been destroyed.
  
• This is the first appearance of Major Hayes and his MACO squad. The MACOs are military and not members of Starfleet.
  
• The Enterprise main theme, "Faith of the Heart", has been remixed with a more country rock feel.