Diary of a Witch is a book found in Dishonored 2.
Transcript
Third Day
Found me a dead man on the beach today, draped in seaweed and jellies. His belly so swollen I feared it might burst if I poke it. Half a dozen crabbies scampered out his open maw. I were thinking I might try me some strong magic. The kind that needs a limb or two for full potency. So I carries one of his legs home. Pulled off easy.
Fifth Day
Foul luck! The angelica bloom was sharp as a sailor's tongue, but still the spell went bad. I don't fathom it, because the leg was big and full of juices.
Eight [sic] Day
Ah! Come to me in a dream what went wrong! That soggy leg I used weren't near enough fresh, and it spoilt the magic. Next time I'll make a deal with the undertaker, and get me a nice recent mort.
Location
The book can be found by the painting of Thaddeus Campbell in the building directly in front of the skiff at the beginning of the mission Edge of the World.