I didn't see "Back in a Tick" as a subtitle. I'm not familiar at all with the book, so based on the cover, and my own misconceptions, I'll just say what it suggests to me.
First off, I think it looks really good. One thing I think MUST be changed is the name. "Dr. Phil Plait Phd." maybe?
That would actually eliminate some of the misconception I have. Based just on the cover as it stands now, It looks like crime thriller about a serial killer that has issues with the lunar cycle. They scythe hanging on the moon means that that's not the right phase. The note indicates that the killer will be back in a bit... to strike again.
Bwa ha ha ha
I do like the look of it, and if I actually knew what it was about, or saw it in the Astronomy section, it might change things. If I saw someone reading it, it would be about a serial killer.
I'm Not Evil.
An evil person would do the things that pop into my head.