This was a Sigma short story featuring the assassin Seichan in a singular adventure. I had a lot of fun reading this story. It's a little on the short side to do the plot justice as the cult and bad guy don't have much opportunity to be a real threat, but the detail of the French catacombs beneath Paris and the action were perfectly entertaining. It has to be noted that stories like this, and 'Tracker' are promotional tools for the related novels. Half of the book for these stories is the excerpt for the follow-up novel.
I don't have a problem with that, personally, as you're getting a short story and a glimpse of what's coming up. It's a win/win and enables the reader to sample the author' style and to see if the story is for them. I know some won't like this, but they're very cheap and at the very least you're getting a highly entertaining short story to read on your lunch break, commute, or wherever.