A fourth signal leads the U.S.S. Discovery to an insular world, where Pike is forced to make a life-changing choice. Burnham and Spock investigate a Section 31 ship gone rogue, leading to a discovery with catastrophic consequences.

Sonequa Martin-Green (Commander Michael Burnham)
Doug Jones (Commander Saru)
Anthony Rapp (Lt. Cmdr. Paul Stamets)
Mary Wiseman (Ensign Sylvia Tilly)
Shazad Latif (Agent Ash Tyler)
Wilson Cruz (Dr. Hugh Culber)
Anson Mount (Captain Christopher Pike)

Mia Kirshner (Amanda Grayson)
Mary Chieffo (Chancellor L'Rell)
Ethan Peck (Lieutenant Spock)
Tig Notaro (Commander Jett Reno)
Kenneth Mitchell (Tenavik)
Rachael Ancheril (Commander Nhan)

Emily Coutts (Lt. Keyla Detmer)
Patrick Kwok-Choon (Lt. Gen Rhys)
Oyin Oladejo (Lt. Joann Owosekun)
Ronnie Rowe Jr. (Lt. Ronald Bryce)
Sara Mitich (Lt. Nilsson)
Ali Momen (Specialist Kamran Gant)
Julianne Grossman (Discovery Computer)
Ian James Corlett (Section 31 computer)
David Benjamin Tomlinson (Lt. Linus)
Byron Abalos (Trainee #1)
Olivia Croft (Trainee #2)

• This episode gives us the first look at the "new" Klingon D7.
  
• The monks on Boreth who are devoted to Kahless also guard the time crystals. Time flows differently for those who protect the crystals, and the timekeeper Tenavik is revealed to be Voq and L'Rell's child. He is played by Kenneth Mitchell, who previously portrayed Kol and Kol-Sha.
  
• The crystals reveal Pike’s future: the accident and his confinement to the chair. If he takes the crystal, his future will be sealed (as seen in the Original Series episode "The Menagerie".
  
• Burnham and Spock find Lt. Kamran Gant alive among the dead on the Section 31 ship. He was the Shenzhou tactical officer before joining Section 31. He was last seen in "The Wolf Inside" as his mirror counterpart.
  
• Gant had been taken over by Control, who lured Burnham to the Section 31 ship to inject her with nanobots so they could use her to obtain the Sphere archive.
  
• Reno was married, but her wife passed during the Federation/Klingon war.
  
• Tilly does not appear in this episode.