The Wig in the Window by Kristen Kittscher

In this funny and clever middle grade mystery reminiscent of Rear Window and perfect for fans of the Mysterious Benedict Society series, Sophie Young and Grace Yang are best friends, seventh graders, and spies.

Sophie and Grace have made a game out of spying on their neighbors. On one of their midnight stakeouts, they witness a terrifying scene at the home of their bizarre middle-school counselor Dr. Charlotte Agford (also known as Dr. Awkward).

At least, they think they do. When the girls are proven wrong, they are still convinced that Dr. Agford is hiding a terrible secret—and they're determined to find out what it is. Soon the girls are breaking secret codes, being followed by a strange blue car, and tailing strangers with unibrows and Texas accents. But as their investigation heats up, Sophie and Grace start to crack under the pressure. Will solving the case destroy their friendship?