The mission "The Surgeon" requires you to do some eavesdropping
The Surgeon is the a mission in Sequence 2 in Assassin's Creed III.
It starts after talking to Thomas Hickey during the segment: "Next on the List"
After leaving the Green Dragon Tavern you will be automatically transported to the Church Residence to the south.
After the cutscene, you need to eavesdrop on Benjamin Church's neighbors. See here for help with this step:
Assassin's Creed III: The Surgeon How to Eavesdrop
Note that Orange Markers indicate caution. Those targets must not be killed. If you need to use weapons, use only non-lethal ones against them. Make sure to stay close to your target to hear all the pieces of information you need.
Eavesdrop on Ben Church's neighbors while hidden