Very high appeal and follows the model of 39 Clues, with a different well-known author for each book and a tie-in to an online game. I thought this first one was okay (and usually Mull isn't a good fit for me, so this is a fairly promising sign). Stiefvater is one of my favorite authors, so I am looking forward to #2. Recommended for readers ages 8-11 who need something fast-paced with a shiny cover.