The Old Diary is a tome in the first act of Diablo III. It is needed to complete the achievement A Quick Study and can be found in a Keepsake Box on the Old Tristram Road or in The Old Ruins.
It reads as follows:
- "There is chaos everywhere, and word in town is that Lachdanan killed the king! If only this is true, perhaps our days and nights of living in terror are behind us now."