What's the Name of That Book??? discussion

So yesterday I saw someone reading this book and I asked to have a look at the back. It seemed really interesting and I went to download it on iBooks and I couldn't remember the name. All I can tell you about the book is that:

The books title is one word starts with an I
On the cover it says 'now you see her, now you don't'
The cover of the book is blue
On the back of the book it says something about being a new age of superheroes.

I know this isn't a lot to go on but if anyone knows what the book is it would be great if you could comment!

Thank you!

I believe it's: -Illusive, by Emily Lloyd-Jones :)

Thank you so much!

You're very welcome x