Sokolov's Note to Howlcreek is a written note found in Dishonored.
When you and your men arrive tomorrow, I'll be working in my greenhouse on the roof. I know the Lord Regent wants you to follow me at every moment, but please avoid disturbing me. The experiments I am conducting are quite sensitive and I must finish with haste.
It can be found inside the main entrance to Sokolov's apartment during the mission The Royal Physician.