Introduction
In Excommunicatis the players are a team of nutcases, misfits and outcasts, brought together by the Catholic Church to keep the people from finding out the truth: There are strange creatures of the night, there are demons, there is a god... Should the truth get out, all those people will end up like you, a damned soul, incapable of Faith as you can't believe in God if you KNOW he exists! Faith loses all meaning then and from that point on all you're doing is working towards your reward, heaven, and thereby unable to enter it.
When they find out it's usually a traumatic experience, they come face to face with something from the shadows, end up unlocking magic powers from mysterious sources or come into debt by some greater power... Some embrace it and end up on the dark side, others go insane a few can sort of handle it, but usually end up dead quickly. Once your eyes have been opened, you cannot close them again and you'll see the creatures as they are, and notice they're all around us. They always have been... And they dislike being seen!
You and your team are the few that have been given a chance, a new lease on life, a way to end up in His good graces again. You've been picked out of whatever madhouse, bolt-hole or hide-out you've been stashed away in, and will get training, equipment and a shepherd to lead you to salvation by stopping those things and thereby protecting the "innocents". The reason you've been picked is due to your training, aptitude or raw skill and after some clever tests (to see whether you'd fit in a team), you've been given a choice after which you shipped off to Rome. Some however have been picked for their skills in the occult, whether they're a Witch and marked for death because they used their powers to beguile a human mind, a Wizard - their spells and lore bought from strange and terrible things that will eventually take their due or a Diabolist (also known as a Sorcerers or Warlocks) - borrowing their powers from a spirit or demon, or passed on from family member to family member.
And if you've dabbled with magic, this is your only and last chance, because the only way out is summary execution. Once you've tasted whatever power you've been given, it will eventually end up in you being a gateway for something horrible to come through into this world. At least this way you'll help your team out until this happens, and when it does they'll be there to send you to the afterlife before whatever is tearing its way through you, gets through!
Even the Shepherd is usually a misfit, a washout, a disgrace to the church, this being their last chance for redemption too! Whatever horrible thing they've done, the Knights Templar are their last chance of salvation. They will learn the truth (if that wasn't at the basis of their crisis) and are thereby damned all the same, and only by assisting the team in a selfless crusade can they purge themselves enough to get another chance at Heaven...