Okay, so apparently there was a problem with the settings in my Pulley account which blocked anyone outside the UK from buying The Thirteenth Floor. I'm assured this has been fixed now, so please try again, and thank you for bearing with me while I try to figure this stuff out.
I thought I'd share a couple of cover roughs I played around with on my way to the final cover. I couldn't make up my mind between them, until my friend and sometimes-collaborator Scott Gray applied his editorial eye to it and pointed out that covers with human beings on them are generally more engaging. Well done, that man - he was right.
I still kind of prefer the rough version to the finished version.