From introduction: The Abaddon Key is a Cthulhu Rising adventure designed for a group of experienced player characters (PCs) who are members of the Interstellar Colonial Marines Special Operations Arm. It was written as a follow-on from [SM03 The Stars Are Also Fire], but with a little modification, a Keeper can run it as a stand alone adventure or insert it into another campaign. Paranoid PCs are guaranteed to suspect mythos involvement in the adventure, and crafty Keepers are encouraged to play this angle up. The fact is that the mythos-like story threads in this adventure are red herrings, and all is as it seems (for once!).