Assassin's Creed 3 Walkthrough Part 36 – Sequence 7: Lexington and Concord

When you are ready, head over there. You will find John Parker standing by ready for you to begin this mission. Talk with him and chaos will begin to unfold.

Head to the Right-hand side of the road, grab the horse and start off toward the marker. You have 3 minutes to get there and it is not a very hard ride, it just looks very dangerous. Spur on your horse as often as possible. You have a fair distance to cover and very little time to do it in.

Once you make it into Concord the first Optional Objective will appear:
Rescue the Civilian Hostage

Just keep your pace and move forward. This is tough only because of the timer over your head. Turn to the left when this objective appears and head for the wooden bridge. Chase after the wagon with the civilians and target the Officer immediately. Ride up and assassinate him followed by engaging his troop and finishing them off as quickly as possible. Getting a kill streak will end this very quickly and make your life a lot easier (meaning it is done in 30 seconds or less, 45 on the outside).

Now resume your run through the waypoints. Once you cross the bridge there is only a short run to the finish. A cutscene begins where the man in charge questions Connor abilities. From there things get sorted out and Connor is placed in charge of 2 firing lines in 3 positions.

Optional Objective
Kill a group of regulars with a single order on 7 separate occasions

Each of these positions allows the patriots to fire on the Red Coats coming from the left-side of the bridge, the bridge or the right-side of the bridge. Connor needs to move between the different locations and give orders as to when to fire. The best time is when the a red hexagon appears above an enemy troops. Be sure that Connor is within the White Circle around each group to ensure that he can give the order clearly.

If you are after getting the optional objective then there is a little more to note. To get the full group kill, you must time the order right. For each of the 3 locations, the spot is different. You want to give the order just after the group moves into optimal range:
Left of the Bridge: After the troops pause at the bank.

The Bridge: When the troops pause in the middle.

Right of the Bridge: After the troops pause at the bank by the fire.

This will continue until 130 Regulars have been shot down. When that has been done, get across the bridge and talk with James Barret. The two have a troubled talk and the memory will conclude. It is time to move onto the final memory of the sequence.