This is a book I read as an adult (after it being highly recommended to me by my own children) and I absolutely loved it. When Jessica begins to turn invisible, she and her friends set off on an adventure to find out why. It turns out that a rose quartz necklace Jessica was given as a birthday gift was reacting to a serum/potion she didn’t know she had accidently come into contact with at birth, and it’s causing invisibility. And Jessica’s not alone – there are others out there who also came into contact with the same experimental serum at birth. Finding them, and finding out what happened, leads her to eventually saving herself and her friends from danger. Fast paced, clever and fun.