If you managed to get by the Parsons State Insane Asylum and killed the mercs there, eventually a ghoul mercenary named Edward Deegan will approach you. He’ll acknowledge your skill, telling you that he tracked you down and will eventually attempt to hire you. You can ask for reward and he’ll tell you to talk to his boss in Cabot House. The location will be marked in your map in case you haven’t discovered it yet.
Walk south and follow the marker to reach Cabot House. Speak in the intercom and say that you’re expected to get in. Talk to Jack Cabot and after some dialogue about precursor civilizations and stuff, Edward will tell you about your job to locate the missing package that was picked up from the Parsons State Asylum.
Head to the Asylum and talk to the guard captain, Maria. When asked about the package, she’ll tell you that the raiders who are responsible are holed up in the Parsons Creamery further north. Head there and clean the place up. Kill all the raiders then loot the Mysterius Serum from their body. Some raider reinforcements may arrive so take them out as well.
Deliver the serum to Edward and give it to him or convince him that the serum’s gone. After that, the quest will be completed after that. He’ll then give you another quest.