A third mystery for thirteen-year-old Agatha Oddly - a bold, determined heroine, and the star of this stylish new detective series.

As the youngest and newest recruit to the gatekeeper's guild, Agatha Oddlow know she's got a lot to prove - not least because her mother was such an important member of the secret society.

So, when an assistant at the National Gallery goes missing, Agatha begins investigating. Soon she uncovers a plot bigger than she could ever have imagined. As Agatha delves deeper and deeper into the mystery, she's not sure she'll ever get to the bottom of it all...