Malchiodi's Diary is a book found in Death of the Outsider.
2nd, Month of Darkness
I am now certain the meaning of that script adorning the flesh of those few who encounter the Outsider. It is his name- the name he lost when he merged with the Void. And if this name is returned to him, the old ritual performed by the Envisioned years ago would be undone.
This revelation sends shivers down my spine. What I hold is the catalyst that could undo everything our collegiate has accomplished.
11th, Month of High Cold
The ancient language tantalized me still. The pronunciation was never formed for any earthly tongue. Perhaps these people, long ago, spoke with the spirits? But speculation is one of the many pitfalls which threatens the errant philologist. To pursue this further would necessitate transgressing the deepest commandment of our order. No one has entered the Ritual Hold since the Outsider merged with the Void. But to find one of those cursed spirits to read this language... It intrigues and frightens me in equal measure.
27th, Month of High Cold
Against all caution, all prudence, all sense of loyalty, I persist. I cannot abandon my research. This place, this reliquary that holds the Outsider's true form, calls to me. If my plan to enter the Ritual Hold is found out, all is lost.
This book can be found in Malchiodi's Chest during the mission A Hole in the World.