Corvo's gear.
Note From A Friend is a written note found in Dishonored.
Transcript[]
Corvo, if you're reading this it means our plan worked and you've broken free from Coldridge. One of our contacts has hidden weapons for you somewhere deeper in the sewers. Grab the gear and find Samuel where these tunnels dump into the river. He will bring you to us.
A Friend Who Will Meet You Soon
Location[]
It can be found attached to the three large crates upon entering the sewers, in the mission Dishonored.