I'm impressed! I have read several books about Alan Turing and this one is now among the best I've come across.
It gives an fantastic overview about Alan Turing's life and work and it does a great job at explaining complicated ideas and theories. It also has some quizzes and 'Try for yourself' sections so that you can test your knowledge. It is obviously aimed at younger readers, but I would also recommend it to adults as an introduction. You can read it in one sitting and if this sparks your interest and you want more details you could read 'Alan Turing: The Enigma' by Andrew Hodges afterwards. Thumbs up for this little book!

Sidenote: I might be wrong, but I think there is a little error in the 'How binary works' quiz in the first edition of this book. 10101011 is 171 in the decimal system, not 169 as stated in the answer. Mistakes happen to all of us of course and I don't mention this to be pedantic, but because doing everything right and as instructed and then being told that you got the wrong solution could demotivate some younger science enthusiasts. And this is certainly not the goal of this otherwise perfect little book