A Book By Its Cover

I've been ridiculously happy with the covers I've had so far for the Maradaine books.  I think they really capture the feel of the books and do an excellent job drawing reader attention.  Paul Young has done right by me here.

You look at the Thorn cover, and you know you're going to get a city-based adventure in a fantasy setting, one that involves a rooftop-running, nighttime focused hero.  You look at the Murder cover, and you know you're going to get something involving gruesome murders and two heroes who are equal partners.  

So, what do you see in the Alchemy cover? Beyond the obvious "this is a sequel to Thorn", since he and the two moons are prominent again.