This movie was originally announced in 2010. Producer Graham King very much wanted Angelina Jolie to play Ruth Slater, and hired Christopher McQuarrie to write a script tailored specifically for her. She never officially signed on, and over the next few years the movie went through various other writers and directors, including McQuarrie and Scott Frank, before stalling. It went back into development in 2019.
The song Katie is playing on the piano is Chopin's Ballad No 1 in G minor, op.23. It is the same song Adrien Brody was playing for the German officer in "The Pianist" (2002).
Was known early in development as "Unforgiven", after Unforgiven (2009), the British miniseries on which it's based, before going through pre-production and beginning filming without a title. It was variously known in trade publications as the "untitled Graham King film" or the "untitled Nora Fingscheidt project". It briefly used the working title "Desire of the Prey" when filming restarted in September 2020. Although titles are not copyrightable under American law, the filmmakers still spent over a year searching for a suitable title, in order to avoid confusion with the Clint Eastwood movie Impitoyable (1992).
The piano music Katie plays at her recital is 'Everything In Its Right Place' by Radiohead