If you've read any of George R R Martin's Song of Ice and Fire books, you know what this one is about already. Quick summary: there are a group of men, mostly criminals and victims of circumstance, who have devoted the rest of their lives to the Wall. A mysterious and old supernatural enemy is returning to threaten the seven kingdoms, but the 'kings' and their armies are too busy with their own wars and politics to take notice. This leaves Jon Snow and the rest of the Night's Watch alone in the cold north to defend against the approaching evil. Hopefully that didn't contain too many spoilers.