Blood Tide

Blood Tide is a quest in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
Cassie Dalton on the docks of Far Harbor wants the Sole Survivor to avenge her family. There are three stages to this quest line. Cassie will pay the Sole Survivor for their efforts and will be very grateful to them.

Cassie talks about the illustrious history of the Dalton family on the Island and how the family has fallen to ruin. She is now the last living member of the family which, according to her, was the wealthiest family on the island for generations.

First, she asks the Sole Survivor to go to National Park campground and eliminate the feral ghouls there to avenge her cousin, Petey. The National Park is northwest of Far Harbor. Once the ghouls have all been killed, return to Cassie for a reward and the next step in the quest. Cassie will give the player character 200 caps, which can be raised to 300 caps with increasing speech checks.

Second, Cassie wants to avenge her grandfather, George Dalton, by traveling to Dalton farm at the northern edge of the island and killing the fog crawler there. The fog crawler can be a tough fight, so be prepared. The Dalton farm can later become a settlement. After slaying the fog crawler, travel back to Cassie at Far Harbor to receive her third step in the quest, as well as 200 caps that can also be increased to 300.

Third, Cassie wants to avenge her husband, Danny Dalton, who was killed by the leader of a gang of trappers located at Brooke's Head Lighthouse, which is fairly far to the southwest, on the shore of the island. There are about a dozen trappers around the lighthouse. Either fight through them or sneak in the back from the ocean. Either way, upon reaching the lighthouse, head up to the top of the winding staircase inside to find Douglas, the leader of the trappers there. Kill Douglas and loot his corpse.

Return to Cassie at Far Harbor to complete this quest for some XP, some more caps, and the legendary pole hook, Bloodletter.