*Story related SPOILERS head*
Successfully hunt down and kill Lee. First chase him through the docks by dodging the exploding barrels/first two enemies by running to the left down the stairs. Keep going straight ahead and you'll come across a firing line of enemies, which are also dodgeable by turning down to the left. Farther on you'll be in a burning building. It will be falling apart inside. To get around this you need to quickly clime the section of wall to the right that just fell down. Chase him till the cutscene and by the end you will both be injured and Connor passes out. Then board a boat and follow Lee to the frontier. Inside an Inn Connor shares a drink with Lee and finishes him with a dagger. 6 months later Connor returns home to the village and speaks once again with the "spirits" (Juno) and she tells you to hide the amulet that is your prize from killing Lee. Connor digs up Achilles grave next to the mansion and drops the amulet where only he can find it.
(Here's a video solution I found on youtube. All credit goes to the creator, theRadBrad)