2.5 stars
My least favorite of the series so far. The pirate captain was too one-dimensionally evil and the "clue" on the treasure map was too ridiculously simplistic for me to give this 3 stars.
It was fun, though, to get to meet the M person. And to learn the purpose of the treehouse and why jack and Annie are able to use it. Although why she would choose a treehouse of all things to use as her time machine is never addressed...