Time travel? A high-tech rock that turns invisible and allows you to talk to people centuries in the future? Ghosts wearing sneakers and old school sweatshirts? A younger sisters falling in love with your best friend? This is not what Jonah had expected when he entered the cave in the first book of the series, Found, but in this better-than-the-original sequel, it's exactly what he gets. Without giving away too much from the first book, I can say that if you're interested in 15th century England, time travel, weeping maidens who are actually plotting revenge on the ruling king, or dead princes from history who are actually being temporarily inhabited by their 21st century selves (yes, it's a bit complicated), you'd love this book. Moreover, if you enjoy historical fiction, science fiction, or writing with unexpected twists and turns, you're bound to enjoy this series by a gifted writer. Yes, the book is as good as its cover suggests!
(After reading this second book, I realized how dull the first book was compared to this, but you really have to read them in order. It's worth it!)