They need to find a way home, then, either through feared seas or across hostile lands. Their journey begins with a betrayal (of their oath to God and the Church) and a theft (albeit from a thief), and thereafter their sins are compounded by lies and duplicities that their poverty forces upon them.
For a while their luck holds; but then they come to a great city, the strangest, largest, richest city in Western Christendom. When one of her citizens, a man of ancient, honourable lineage, is murdered in the streets, the failed crusaders discover that their sins have been marching with them, step by step, and now demand a reckoning.