When a new signal appears over Saru's home planet, Burnham, Saru and the crew embark on a perilous mission that puts Saru in danger and raises questions about the Red Angel's intentions. Hugh struggles to come to terms with his new reality.

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)

Javier Botet (Old Creature)

Hannah Cheesman (Lt. Cmdr. Airiam)
Emily Coutts (Lt. Keyla Detmer)
Patrick Kwok-Choon (Lt. Gen Rhys)
Oyin Oladejo (Lt. Joann Owosekun)
Ronnie Rowe Jr. (Lt. Ronald Bryce)
Hannah Spear (Siranna)
Julianne Grossman (Discovery Computer)
Mark Pellington (Ba'ul voiceover)
Raven Dauda (Dr. Tracy Pollard)
David Benjamin Tomlinson (Lt. Linus)
Michael Ayres (Transporter Officer)
David Benjamin Tomlinson (Kelpien Villager #1)

• "Agent Ash Tyler" now sports a Discovery command uniform with a black Section 31 badge.
  
• With his threat ganglia gone, new tissue resembling spikes is growing in their place. Dr. Pollard summizes his fear response is also being repressed.
  
• This episode shows our first look at the Ba'ul, the predator species of Saru's home planet, Kaminar. They live under the planet's oceans and achieved warp 20 years prior. The U.S.S. Archimedes made first contact with the Ba'ul. Lt. Georgiou served on the Archimedes.
  
• Airiam retrieves historical data from the Sphere on Kaminar. 2300 years ago, the Ba'ul were the prey species… until they gained a technological advantage and completely wiped out the evolved post-vahar'ai Kelpiens, leaving only the unevolved.
  
• Saru uses the sphere signals to accelerate vahar'ai to all Kelpiens. Before the Ba'ul can destroy the villages, the Red Angel appears and disables the Ba'ul. Saru and Siranna witness the Red Angel. Saru is able to determine that it's a humanoid in a mechanized suit.
  
• Tyler mentions Control — Section 31's threat assessment artificial intelligence.
  
• Hannah Spear (Siranna) first appeared in the Short Trek "The Brightest Star".
  
• In addition to his role as Lt. Linus, David Benjamin Tomlinson reprises his role as a Kelpien Villager from "The Brightest Star".