This is the best Emily power we have seen yet. This gives you the ability to connect and line up the faiths of your enemies. What this means is that whatever you do to one enemy will happen to the rest. So, as in a 'Domino Effect', one domino enemy falls victim to your powers and so do the others if they were aligned properly.
At the start of Mission 2: Edge Of The World, proceed through the Bloodfly infested building to the upper floor. You will find an infected enemy and the key to the Black Market shop. Collect the key and return to the Black Market at the start of the mission. Climb through the window behind the shop and open the door with the key to get the "Black Market Burglar" achievement.