What if Call of Cthulhu, but simpler and with a traitorous Heretic?

I've been interested for a while in games about eldritch horror and paranormal entities - games where "magic" was something frightening and dangerous, not just a list of reality macros to be run by rote. Investigative games also tickle my fancy. In media, I liked the themes of X-Files and Warehouse 13 and Eureka as well as It and Magicians and Grail. I also like the premise of Paranoia RPG, and really enjoyed the play-by-post game of it I lurked on. But I noticed that the game I watched used Risus to run faster and wackier than the original rules could enable.

Simplicity in game design, with any involved mechanics being targeted right to a central theme, is always good. That's why I based this game on the 24XX engine.

The "Sanity" mechanic in Call of Cthulhu is well-intended, but I don't think is sensitively named and also just isn't quite impactful enough for my tastes. I wanted something more immediate in effect. I also, convergently, wanted a way to make "magic" available to the players' characters but expensive in a very meta-gamey way that the players, as well as the characters, would notice. So I came up with the Composure die in Heretic. It's kind of like a usage die for paranormal interactions, whether that's the eponymous Heretic bending reality, or the other characters trying to invoke or abjure an entity. When it runs out ... your mind gets eaten. You don't have to simulate any kind of mental illness or neurochemical imbalance or delusion or whatever. You're just done.

The rest of the game hangs on the Composure die and provides a context for players to make decisions about what their characters will do, as well as a solid reason for all the characters to work as a team: because they are a team, employed by the government, with a specific mission to enact in each episode. In that context, it seemed interesting to have one of the players (or possibly an NPC) be a Heretic, a traitor to the team who's cut a deal with an entity in order to attain supernal powers. That concept sprang directly from Jason Tocci's 2400: Codebreakers, in combination with the aforesaid Paranoia RPG.