How to Acquire
Farley Havelock can be found in the Lighthouse staring at the fire in his chambers, where Corvo can proceed to choke him out. This is helpful in achieving Ghost and Clean Hands. Emily will be inside the door to the right of the mantle.
After getting past the showdown between Treavor Pendleton and Teague Martin, Corvo will be able to ride the elevator up to the tower. Havelock will be on the catwalk at the very top of the tower, holding Emily to his chest, saying he will jump. By saving Emily from both Havelock and falling, he can unlock the achievement.