Mysterious holotape is a holotape in the Fallout 4 add-on Far Harbor.
Locations
The holotape is on Douglas, a trapper leader at Brooke's Head Lighthouse. It is only found during the quest Blood Tide.
Transcript
Unknown Speaker: Well, that settles it. I am one hundred percent screwed. Damn this fog. You'd think a lighthouse would be easy to find, but not in this. Never seen fog like it. Can't believe I let myself get talked into this. How do I know that woman wasn't crazy? I'm starting to think her whole story was some fantasy she cooked up to get attention. Taking out one trapper to avenge her husband's death... it sounded easy enough. Now I wish I'd stayed far away from this godforsaken island. Shit... something's coming.