To gain this achievement, you need to take hostages in a heist, preferably before the police assault. You need at least 1 other human player for this - make sure you equip the '42nd' mask through the Inventory beforehand. When the other player(s) have been taken into custody, hold out until the end of the assault. You should gain the ability to trade a hostage to release one player. Do this 7 times while wearing the mask, and you get the achievement.