Okay 3 things I realized about the cover illustrator Clyde Caldwell. Firstly, he loves boobies. Secondly, he didn't read the book because Tinker is 18. Which leads to my third point, the woman on the cover is no where near 18 - probably late 30s - and Clyde must be in love with her to put her on the cover even though she much older than Tinker.
I love this series. I can't remember who first turned me on to it, but it's just wonderful. Elves have found a home in a Pittsburg that's actually part of their world but with all the buildings, streets, etc., and then once a month humans were able to go back and forth until Tinker tried to stop some baddies and everyone got stuck. This is them all trying to figure out how to live together when other people are trying to drive them apart. I'll keep reading the books in this series as long as the author wants to write them.