Letter to Lieutenant Valiente is a written note found in Dishonored 2.
I keep thinking of what you told me. If it's true, if that's really what you saw. I just can't bring myself to believe it, even though I trust you entirely.
I know Duke Luca is a despicable person, but him using that monster for his political agenda? Please, I beg you, don't be rash, I know you want to resign from the Grand Guard, but I fear for your life as long as you're in Addermire. Don't send that letter yet, don't talk to anybody about what you saw, at least until you come back home and we can discuss it with clearer heads.
Please stay safe. I'll be waiting to hear from you.
It can be found on the second floor to the right of the main entrance of the Addermire Institute, next to the dismembered body of Valiente during the mission The Good Doctor.