Mannequins will rise out of the ground around the map. There are three mannequins that are glowing blue. Find one and interact with it. You will need to defend the area against the attacking undead. Once completed, you will be able to pick up a mannequin piece. You will need to repeat this step for each of the three blue mannequins. Eventually, the player will have three blue mannequin parts. Place all of them on the broken mannequin in front of the APD.