Letter to Callista is a written note found in Dishonored.
Callista, fret not. I believe there is still hope for Emily and Dunwall. I don’t believe Corvo is gone. I’ll be searching the river for him, but if you catch wind of him, shoot up a flare using the launcher I placed in Emily’s tower and I’ll make my way back as quickly as I can. Keep this tower locked and take care of yourself. Emily is gonna need you when this is over.
While this note is always found during the mission, The Loyalists, its location differs depending on Corvo's chaos level. In high chaos, the note will be found in front of the Hound Pits Pub with Callista's dead body. In low chaos, both Callista and the note can be found in Emily's Tower, where Callista flees after being spared by Havelock.