After completing the main quest Institutionalized but before The Railroad quest Precipice of War has begun, Desdemona will inform you that Coursers from The Institute have been located, and sends you to Ticonderoga Safehouse. If you trigger Precipice of War after accepting this quest, this quest will fail. It is an unmarked location on the map, south of Monsignor Plaza in the Cambridge Neighborhood.
All you need to do here is dispatch the 2 Coursers here, including the leader X9-27 and can ignore the rest of the enemies if you wish. Do the deed and return to Desdemona for your reward.