People who love math and puzzles, this is perfect for you!

I couldn't put it down.

Great and interesting read

It was so good I want the next book in the series!!!!!!!!!!!!

I liked this book because it had a lot of action and mysteries to solve. Charlie reunites with her brother and they must solve a case that Einstein designed so that only a high IQ person could figure it out. Even though Charlie was only 12 years old she was able to be helpful and useful and proved to be a good person in her brother's eyes.