Corvo's gear.
To the Lord Protector is a written note found in Dishonored.
Transcript
Greetings, Corvo. Or should I say Lord Protector, as you were known before that title was wrongfully taken from you.
We are servants of the Empire and of the true Empress, a group of loyalists who want very much to meet you. Take these weapons, crafted for you from the finest materials in the Isles, and meet with our man, Samuel, near where these tunnels spill into Wrenhaven River.
All haste and luck. We share a common purpose.
Location
It can be found in the Dunwall Sewers on top of the supplies chest during the mission Dishonored.