"Terra Firma" is the ninth and tenth episodes of the third season of the American television series Star Trek: Discovery. The two-parter begins in the 32nd Century, and follows Emperor Philippa Georgiou as she returns to the Mirror Universe. The story for both parts was written by Bo Yeon Kim, Erika Lippoldt, and Alan McElroy. The teleplay for the first part was written by McElroy, with Omar Madha directing. The teleplay for the second part was written by Kalinda Vazquez, with Chloe Domont directing.
Special guest star Michelle Yeoh portrays Georgiou alongside series regulars Sonequa Martin-Green, Doug Jones, Anthony Rapp, Mary Wiseman, Wilson Cruz, and David Ajala. The two-part story writes Georgiou out of the series, setting up a potential Section 31-based spin-off series starring Yeoh from writers Kim and Lippoldt. It does this using the Guardian of Forever from Star Trek: The Original Series, with guest star Paul Guilfoyle portraying a personification of the Guardian. The episodes return to the Mirror Universe for the first time since the first season, allowing costume designer Gersha Phillips to make improved costumes for the setting. Filming took place in Toronto, Canada around December 2019, and included location shooting in temperatures below freezing.
The first part was released on the streaming service CBS All Access on December 10, 2020. The second part was released a week later on December 17. Both parts received mixed reviews from critics.
Plot
Part 1
Kovich, a mysterious Starfleet operative born in the 3100s, explains to Hugh Culber that because Philippa Georgiou has travelled through time and dimensions, her molecules have become too unstable and will decay. Culber learns from Zora, the ship's computer, that Georgiou has a possibility of survival if she beams down to the surface of an uninhabited planet named Dannus V to find a cure.
Paul Stamets and Adira can trace the Burn to a specific nebula's source and recognize it as a Kelpien starship's distress call. Now on Dannus V's surface, Georgiou and Michael Burnham encounter a mysterious stranger who reveals himself as Carl. Carl shows Georgiou a door, which he says is a portal, prompting Georgiou to hesitate about going through initially. Carl convinces her to cross, and Georgiou finds herself in the Mirror Universe, on board the ISS Discovery, during the time before she visited the Prime Universe.
After resuming her duties as Emperor of the Terran Empire, Georgiou discovers that her time in the Prime Universe had changed her. Michael Burnham betrays her, but Georgiou decides to spare her life under the guise of ordering subordinates to torture her in an agony booth.
Part 2
Georgiou tries to convince Burnham to rule the Terran Empire faithfully by her side, but Burnham ignores her, refusing to speak or eat from her prison cell. Georgiou resolves to torture Burnham until she pledges her alliance to the Empire. Initially, this does not work, but Burnham decides to go along with her adopted mother. Georgiou orders her to kill all of her former co-conspirators and Gabriel Lorca's spies. After finding one of Lorca's henchman in orbit of Risa, Burnham executes him in the brig and reveals her guise to assassinate Georgiou.
The two engage in a fight. The battle mortally wounds Georgiou and Burnham. Upon closing her eyes for the final time, Georgiou finds herself back on Dannus V. Carl then informs them that he is the Guardian of Forever and that he closed his portals to normal humans during the Temporal Wars. He also claims that Georgiou's experience was a test that she has passed and can be given a second chance in life.
The Guardian opens up another portal for Georgiou to go through, and she and Burnham bid farewell; Georgiou is sent to a time when the Prime and Mirror Universes are more aligned so she can survive. On Discovery, Book wishes to be useful aboard the ship and provides Emerald Chain technology to assist the crew with locating the nebula where a Kelpien distress call is originating. Later, the crew holds a small service for Georgiou.