Meet with Paul Revere at the Boston pier.
Optional objective: Do not trigger open conflict.
After a longer cutscene you will find yourself on a horse and will have to ride in the direction pointed by your companion. Press the Assassins Guild button from time to time to make sure you're going the right direction. In order to avoid fights, avoid the patrols or wait for them to move along.
After you reach the village, get off your horse, wait for the British soldiers to move a bit further and use Eagle Vision. You will have to knock on the shining door.
Do the same thing in the next village. If you come across a stream on your way, search for a ford and cross it there.
Optional objective: Reach Prescott's location within the given time - 2:00.
Optional objective: Completed all the constraints in one playthrough.
The third village is found right across the bridge.
As only you knock on the door of the manor there, you will be attacked by British soldiers.
You will have to escape to riding as fast as possible to the green zone marked on the map. Prescott's house is found there. In order to lose the chase, take a sharp turn right at the fork nearby the stream.
A few meters further you should ride off the road and through the ford. When the enemies stop chasing you, Prescott's manor will be once again marked on the map.
Find the manor using Eagle Vision and knock on the door.
After a short talk, start riding from one point to the next until you reach Adams. There the mission will end.