This adventure is the first part of The Apostasy Gambit trilogy, but it works quite well as a stand-alone adventure, although you might want to tweak the final revelations to suit whatever you will be doing next, as they lead into the next part, The Church of the Damned. As you can imagine from the names, it centres about evil lurking at the heart of religious institutions which the Acolytes will have to uncover and thwart if peace and order are to be maintained.
There's a good backstory to help the GM understand what is going on, suffice to say that like so many things, it all began with well-meaning but misguided individuals who wanted to save, rather than destroy, the Calixis Sector. The adventure itself breaks down into four major sections.
The first part sees the Acolytes involved in regular Inquisition activity, sent to raid the estate of a noble who has gone to the bad and amassed a whole load of dangerous texts and artefacts... one of which should lead them to realise that they need to visit a place called the Haematite Cathedral, where an even greater evil lurks and must be eradicated. It starts almost in media res, with little time for more than a quick visit to the armoury to gear up before the party finds itself leaping out of a Valkyrie transport with grav-chutes, crashing through a glass roof as the raid begins. Notes for scaling combat encounters are provided to accomodate various levels of characters, and other advice is provided as appropriate to help you keep things on track.
The rest of the adventure, which is fairly free-form in nature, covers the exploration of the Haematite Cathedral and investigation of what's actually happening there. It's set up so that the Acolytes can choose their own approach and route through the place, with plenty of activity, events and discoveries awaiting them whichever way they turn. Eventually, climactic events will ensue leading them to discover terrible dark secrets... secrets that leave death and destruction in their wake.
The adventure mixes investigation and combat well, with plenty of activity to keep the Acolytes on their toes. As well as the central theme of secrets to be discovered, it also deals with moral corruption, ill-advised alliances and sheer desperation. The discoveries to be made are spectacular and awe-inspiring if well-handled, and the resources provided should enable you to describe them appropriately.
There's an impressive Appendix of hand-outs and maps, although some are a bit jumbled and the page borders remain - these rather spoil the illusion and you may want to cut the various documents and maps out (if you are using print-outs from the PDF - just what you do with a print version is left up to you, most people don't like ripping pages out of a book).
Overall it is an exciting adventure from start to finish, one that should give the Acolytes a real sense of discovery, of making progress as they investigate... and a good lead-in to the next events you have in store for them.