how can missy and the master be in the same place
The Master (Doctor Who) Gomez' final series in the role was series 10, airing in 2017.[45] Early in the series, the Doctor explains to his companion Bill Potts (Pearl Mackie) that he is guarding a vault on Earth as a result of a promise,[46] which is revealed by a flashback in "Extremis" to be a promise to watch over Missy, who is captive in the vault after the Doctor spared her from execution on a faraway world, and Missy promised to become good.[47] In "The Lie of the Land", the Doctor's crew visits Missy in the safe to gain intelligence on an enemy she had defeated in the past. Her demeanour seems little changed and she has low regard for human life, but in the episode's coda, she sheds remorseful tears for all the millions of deaths she has caused.[48] Missy's gradual reform is indicated in several more episodes. In "Empress of Mars", she returns the Doctor's TARDIS to Mars to rescue the Doctor and Bill; in "The Eaters of Light", she has been released from her cage by the Doctor to run repairs on his TARDIS, which is isomorphically locked so that she cannot pilot it. The Doctor attempts to test Missy's reformation in series finale "World Enough and Time"/"The Doctor Falls" by sending Missy, Bill, and Nardole (Matt Lucas) on a rescue mission aboard a space ship experiencing time dilation near a black hole. However, they soon run into Missy's past incarnation aboard the ship, where the Master (John Simm) has initiated the genesis of new Cybermen. Trapped aboard the ship together, Missy finds her loyalties torn between her promise to the Doctor and the lure of her old self. After initially betraying the Doctor, she later chooses to stand alongside him against a Cyberman army, stabbing her past self and sending him back to his TARDIS to regenerate, concluding her life has led to her becoming the Doctor's ally. Enraged at the idea of ever becoming the Doctor's ally, the Master shoots Missy with his laser screwdriver, disabling her regeneration and seemingly killing her.