Who: A banshee.
Location: Her lair, a few miles outside Conyberry.
Session 4:
Sister Garaele wants the party to find Agatha and inquire about a legendary spellbook.
At our table: The party met Agatha (GM-reported, session gap 6/30-7/28). She told them she gave the spellbook to someone many years ago. She said an heirloom dear to her lies in Thundertree, and offered each of them a magic item if they bring it to her (see Mirna's Heirloom).
At our table: She recognized the Silver Rowan Pendant (described by the party, clasp "Until the stars fade") as her mother's, which went to her younger sister, and offered one Uncommon magic item for each party member to bring it from Thundertree. See Silver Rowan Pendant.