Ronnie Shaw shows up at The Castle. She was a high-ranking member of the original Minutemen before they splintered. She knows what’s behind that heavy metal arm on the North wall… it’s the old armory. However, with much of the castle being in disrepair, they’ll have to find some sort of alternate route inside.
Completing this quest has an amazing benefit for your adventuring as you’ll see from the end of the video.