Nat's little sister, Ella, can be a real pest, so Nat usually tunes her out -- especially when she goes on and on about her favorite mystery series, The Mighty Thompson Triplets. Nat and her friends live mysteries all the time -- they don't need to read about them. But then mysterious events surrounding the school snowboarding club seem suspiciously like a Mighty Thompson Triplets Mystery. If only Nat and the crew could find a copy of the book, then they could get to the bottom of the real mystery -- before it spells disaster for the club.