I am looking for mystery stories that are really hard to guess, but not ridiculous as far as the twist go. Yes, I have read most of Agatha Christie's works.
Angels & Demons is a really good read.
The Boxcar Children.
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Read most of those book too when I was six.
Well I used to read these a while back when I was younger, but they were good then, maybe you would enjoy them.
Its the danger.com series, about 9 books, by Jordan Cray
Rising Sun by Michael Crichton. There's a couple pretty good twists. Just an awesome book, really.
The City of Ember
Spy X: The Code (continue with the sequels)
VELOCITY