Tune in to the familiar frequency of Valentine's Detective Agency Radio station to begin your next adventure. Head over to the office and speak to Ellie who will brief you on a missing girl named Kasumi.
Travel to the Nakano Residence which is north of The Museum of Witchcraft. If you brought Nick Valentine with you, you can find out more about Kenji Nakano's history with him.
Find out the details of Kasumi's disappearance from Kenji and Rei. Investigate the Nakano Residence to find six holotapes with various project notes and one about her dreams under her bed.
Speak to Rei again and ask for details about Kasumi. Using your charm to press further when she hesitates will reveal that Kasumi started staying in her grandfather's boathouse late into the night. Search the boathouse for a safe. Use your lock-picking abilities, or the note on top of the safe will reveal a key hidden in a picture frame. Listen to the holotape.
Talk to Kenji, who will lend you his boat, and you'll begin your journey to Far Harbor.