Start this quest by talking to Father. With the beryllium agitator in hand, the only outstanding issue is the talent and experience necessary to power the Institute reactor. That includes a scientist named Wallace, who is holed up in a house in Greygardens.
The resistance you'll face depends on a couple factors. If you haven't met The Minutemen yet, you only need to deal with some Gunners. If you have any kind of relationship with The Minutemen, you'll find them outside the homestead waiting to attack. If you authorize this attack, all future Institute missions will be locked out. This will trigger the Banished from the Institute quest, where you simply have to elude all nearby characters loyal to The Institute.
Assuming you'd like to continue The Institute storyline, tell The Minutemen to stand down and be sure not to kill any Institute forces.
When you've made it inside the homestead, talk to your contact Enrico Thompson. He'll tell you that Wallace has locked himself behind a door.
Make contact with Wallace by talking through the door. Whatever the conversation outcome, the quest will resolve with Wallace joining to The Institute by force or otherwise.
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