An old boyfriend of Hammerlock’s was hired to wipe out the Stalker population and tried to write a book about his adventures. Hammerlock wants you to find the chapters of this book, so he can plagiarise them for his own. The pages of the book will be found in the Stalker piles, similar to the ice things you likely broke during your encounters with Bullymongs.

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The ECHO recorders are completely random, so you'll need to keep checking out the Stalker "piles" across the map.

There is also an optional objective in this mission, which is to simply kill a total of 15 Stalkers. Since you will be going into the territories of Stalkers, you will come across many of them, although you may get the five chapters rather quickly. Also, it should be noted that you can kill Stalkers anywhere you can find them and not just in The Highlands, such as in the Captain Scarlett DLC. You can turn in the mission at a mailbox in Overlook.