That Which Does Not Die is a d20 System scenario for 3rd- to 5th-level characters. Part of AEG's Adventure Keep line of short, cheap modules in half-sized format (4-1/4"x11"), it is intended to be run as a single session. Intended for use with the Undead sourcebook. From the back cover:

It's a simple bodyguard job. The threat level is low, and the pay is good. That's what the merchant said when he hired you. Then the bodies started showing up, and every indication that your employer is next, along with anybody associated with him — like you. Suddenly, the job seems a lot more complex.

Everybody makes mistakes. It's a part of life... and death. But when one of those mistakes leads to murder, it's up to you to clean up the loose ends. Because the murder didn't quite take, and now you're stuck right between a single-minded undead revenge machine, and its prey. It doesn't eat, it doesn't sleep, it doesn't negotiate. It kills. And you're right in front of the next target. The term "underworld connections" just took on a whole new meaning.