After the conclusion of The Secret of Cabot House: Emogene Takes A Lover quest, meet Jack outside Parsons State Insane Asylum. Raiders have taken over the facility, and you're tasked with helping Jack regain control of the place.
First help Jack reach his office. Then help him reach the basement. Expect a lot of resistance from Raiders. You'll discover that the Raiders are trying to free someone named Lorenzo Cabot. Follow Jack's instructions pertaining to the generators. He hopes to subdue Lorenzo. Listen to Lorenzo's voice if you wish to be persuaded to go against Jack.
If you decide to put Lorenzo to bed, speak to Jack after and return to Cabot House a week later for your reward.
Alternatively, you can set Lorenzo free. He'll make a beeline for Cabot House. You can either save the Cabot Family and get a different reward from Jack a week later, or you can join Lorenzo and take out the Cabot Family. Doing the latter will reward you with a mysterious serum.