Discovery ventures to the Verubin Nebula, where Burnham, Saru, and Culber make a shocking realization about the origin of The Burn as the rest of the crew faces an unexpected threat.

Sonequa Martin-Green (Commander Michael Burnham)
Doug Jones (Captain Saru)
Anthony Rapp (Lt. Cmdr. Paul Stamets)
Mary Wiseman (Ensign Sylvia Tilly)
Wilson Cruz (Dr. Hugh Culber)
David Ajala (Cleveland Booker)

Oded Fehr (Admiral Charles Vance)
Ian Alexander (Gray Tal)
Blu del Barrio (Adira Tal)
Bill Irwin (Su'Kal)
Janet Kidder (Osyraa)
Tig Notaro (Cmdr. Jett Reno)

Emily Coutts (Lt. Keyla Detmer)
Patrick Kwok-Choon (Lt. Gen Rhys)
Oyin Oladejo (Lt. Joann Owosekun)
Ronnie Rowe Jr. (Lt. Ronald Bryce)
Avaah Blackwell (Lt. Ina)
Raven Dauda (Dr. Tracy Pollard)
Nelu Handa (Smiling Starfleet Lieutenant Holo)
Andrew Hinkson (Regulator)
Jinny Jacinto (The Monster)
Fabio Tassone (Book's Ship Computer)
Robert Verlaque (Kelpien Elder Holo)
Danny Waugh (Vulcan Holo)

• Discovery finds a planet made of dilithium inside the nebula, the source of The Burn.
  
• Su'Kal is the son of Dr. Issa, who left the distress call.
  
• The away team beams into a holographic simulation, which changes their appearance. Burnham appears to be Trill, Culber appears to be Bajoran, and Saru appears to be human — and Doug Jones appears without his prosthetic makeup.
  
• One of the programs in the simulation shows the induction of Kaminar into the Federation — under the united Kelpian and Ba'ul Alliance.
  
• Robert Verlaque (Kelpien Elder) also played Saru's father Aradar in the Short Trek "The Brightest Star".
  
• Avaah Blackwell plays the uncredited Osnullus bridge officer background extra, appears here as human Lt. Ina, seemingly taking the place of Lt. Nilsson.