From the back cover:
"The Sentinels are a group of 'monitors': mortal humans who know about Immortals and keep an eye on them. But the Sentinels are much worse than mere monitors. They are deadly hunters, devoted to the destruction of Immortals.
Sentinels: Mortal Enemies includes:
New NPCs! New weapons! A master weapon list for Legacy Adventures & adventure seeds!
Conversion notes for Fudge, Fuzion, and Action! System"