This quest becomes available if you’re still allies to the Institute and upon discovering Acadia in the island. Take note that doing this quest, you’ll lose access to the quests tied to the NPCs in this location. If you still want to push through with this quest, make sure to complete all other Acadian quests first.
First, speak with Dr. Moseley from the Advanced Systems division and inform him about the existence of Acadia. Moseley will dispatch a recovery team that will capture the escaped synths to be “re-purposed”.
Travel to the staging area near the island’s Rayburn Point. Talk to Moseley to get the attack started. Once you’re in Acadia, shoot everyone. Named synths can’t be killed since they’ll be carried back to the Institute. After the attack has finished and everyone else is rounded up, talk to Moseley to complete the quest.