Only the Good Spy Young, by Ally Carter, Bk 4 in the Gallagher Girls series

In the previous three books in the series Cammie aka Chameleon Morgan has found out how serious being a Gallagher Girl is.  In the beginning it was fun knowing that she was a spy-in-training, sneaking out to meet a townie boy in Book 1 and using their special skills at detection, evasion, invention and deception to learn more about the mysterious boys from Blackthorne Academy in Book 2. 

Incarceron, by Catherine Fisher

Finn is a "cell-born" member of a Scum gang in Incarceron, the living prison with millions of electronic eyes and torture chambers, designed to recycled and re-use everything, even the people who are imprisoned there.  Finn remembers nothing before waking up in a cell, apparently remade from DNA of others who died, but his flashes of memory of the outside world convince him that he belongs outside.

White Cat by Holly Black, Curse Workers, Bk. 1

It was extremely hard not to read ahead in this book because I wanted to know what was going to happen next.  Little clues and pieces of info get scattered out like breadcrumbs, drawing you on, making you want to keep reading.  I figured out some of the twists before they came, but not all, and not too much before they were revealed.

It's a Mall World After All by Janette Rallison

Charlotte has a grudge against her best friend's boyfriend because of how he treated her in middle school, teasing her and making her life miserable.  As seniors now, Charlotte is convinced that Bryant is cheating on Brianna, and spies on him to prove it.  Instead of finding hard evidence of cheating, she keeps getting herself in embarrassing (and messy) situations, usually involving Colton, a guy in many of her classes, president of the National Honor Society club she belongs to, and also the guy who is Bryant's best friend and convinced he isn't cheating.  Charlotte has to face her own prejudices against Bryant and hope Colton and Brianna can get past their preconceived notions of Bryant's honesty in a light and fluffy book about high school and friendships.  A sub-plot in which Charlotte helps a little boy get shoes for his mom by organizing a Christmas gift drive offers some real heart, and Rallison's writing offers real opportunities for laughing out loud.

SLJ recommendation for grades 6-10