- Imperial City Waterfront in Dareloth's house, on desk on second floor (complete the Thieves Guild quest line for access).
- Twilight Sepulcher – a short distance after completing the trial that requires the Dragonborn to extinguish the torches on either side of the Nocturnal statue, take a left which leads to a large room with a stairs down to some loot including potions. The book is on the desk among them. (Requires: Darkness Returns quest to access).
- Howling Wolf's Folly (unmarked location) – On the corpse of a Stormcloak Soldier.
- Faldar's Tooth – at the top of the tower on a table.
- Next to a fallen birch tree down the path from the Troll Den Rkund, an unmarked location.
- Cidhna Mine – On a bookcase in the room with the Prisoner Belongings, and Evidence chests.
I have encountered many thieves whose sole interest in locks is how to open them and thereby pilfer the protected contents of the room or chest. I have taken it upon myself to devise a system of locks that can defeat suchintent.
The materials used to create a lock are of utmost importance. Shoddy brass or copper will give way to a well placed kick, thereby rendering the lock itself useless. I recommend steel over iron when choosing a material. More robust materials tend to be prohibitively expensive and necessitate the door being made of similar metals. I have been chagrined to stumble across the shattered shell of a wooden chest, dwarven lock intact and still locked.
Once these basics are settled, pay particular attention to the offset of the tumblers. A seven degree offset to the keyhole will allow a torque style key to work smoothly, while at the same time causing numerous headaches for the thief attempting to insert non-torque lockpicks.
In similar fashion, the springs of the tumblers should be made by different smiths. Each smith will unknowingly create a spring with different tension than his fellow smiths. This variance will also create difficulties for anyone attempting to pick the lock.