Kid in a Fridge

A bit SE of Jamaica Plains and SW of University Point, there's a ruined house by the road. If you get near, you'll hear a voice coming from a fridge. Shoot the handle open and you'll meet a young ghoul named Billy. Billy's home is marked west of Poseidon Energy and SE of Quincy Ruins.

Walk all the way there and shortly, you'll encounter a Gunner named Bullet. He'll offer to buy Billy. You can sell Billy (increase the selling price by passing Charisma speech checks) or kill Bullet then talk to Billy again to continue escorting him. Remember that if you failed any of the speech checks, Bullet will call the deal off.

Follow the main road until you reach the Peabody House. After the reunion, if Bullet is still alive, he'll demand for the entire ghoul family. Head to his position and talk to him. You can offer selling the family or flat out decline his offer and kill him and his comrades. After taking them all out, talk to Matt to complete the quest and receive your cap rewards.