Edit statutes -> statues *
3 + 4 Leads and Dead Ends
Leads should be the beginning links of chains of causality coming from the hook. These should be extremely suspicious. Let's actually write something, as practice. The hook is going to be "Art Stolen from Small Art Gallery", but to make it interesting, it turns out the art that was stolen was an ornately carved bowl from a newish artist in the area. Part of the ornamentation on the bowl was composed of words that spelled out a sentence in a language not commonly known. What does it do to those who read it? Who knows? Who cares?
†This has a pretty easy set of leads, pieces of stolen are show up in different places, possibly during gruesome accidents or murders. But before we flesh those out, let's talk about Dead Ends. I'm not sure of the significance of them beyond not having to tie all the story elements together while still delivering some good hits.
‡The book recommends 3-ish leads so let's go with nearby murder on the street where someone was drained of blood (and that blood was used to fill the bowl, which the players won't know yet), pieces of some of the statues of the gallery have show up in scrap markets, and some poetry engravings turned up at another murder downtown. Obviously the statues and the poetry are dead ends, so they need to be spruced up. There is also the additional problem of the intro. ie why are the agents here?
I'm pretty confident that for a good story, there needs to be a good beginning and as of yet we don't have a reason why the agents would be sent on an assignment out to a small art gallery, so let's take one of the leads. Say the poetry had some lines from The King In Yellow. Maybe the author was selling it as such. This ties into common-ish knowledge and provides a credible reason for investigation. This should get the story set up like so:
To make things more interesting and/or make things less linear you can start to draw lines between the threads. This creates some flexibility. It kind of feels like overkill but I assume by planning this out, you'll have a stronger base to improvise with.
5 Creepy Moments
Scary is hard to get right and I imagine this needs to be practiced. Or stolen outright from other sources. Given that the bowl is the focus, something should probably happen there. Maybe while investigating the alley reality starts to warp and the corpse begins to speak to them. Another one could be the author reenacting part of The King in Yellow before striking out at a victim. Then let's sprinkle in a monster attack and have the the true burglars try and take the people hocking the statue out of the picture with a summoned beast.
6 Events
For this you should ask yourself what would happened in this timeline if the players weren't here first, then what would happen now that the players are here. Luckily the above diagram has 3 events built in: the ritual, killing the statue people, and the author. We could also have the gallery owner pull up some more information just in case, maybe they pull the tapes and see a suspicious person.