Missy's trial

was put on trial for her "crimes against the universe throughout all [her] lives". However, she talked her way out of being sentenced for the events of The Year That Never Was by pointing out the Tenth Doctor's undoing of those events, and for the murder of Petronella Osgood by pointing out that two Osgoods were still working for UNIT. She then pointed out she had already been punished for her actions at Devil's End, and cleared up confusion about her involvement in the Death Zone by reminding everyone that Borusa was the culprit on that occasion. She was, however, eventually sentenced to death for pushing a girl into a volcano on Riga-Priam. (PROSE: Missy on Trial)

In accordance with their Fatality Index, the Twelfth Doctor was chosen to carry out Missy's sentence. However, he sabotaged the execution machine so that she was knocked unconscious instead of being killed. After swearing an oath to guard Missy's "body" for a thousand years, the Doctor scared the executioners away and had Nardole place her inside a Quantum Fold Chamber. (TV: Extremis)