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.