Effie Truelove and her school-friends Lexy, Wolf, Maximilian and Raven must use their magical skills to defeat the Diberi, a corrupt organisation intent on destroying the worlds at Midwinter.

But during a visit to the Otherworld, Effie is mistaken and imprisoned for being a galloglass - a dangerous, selfish islander.

Meanwhile, Lexy is threatened by the vile professor Jupiter Peacock and Wolf embarks on a perilous journey to find his missing sister. And back at school, Neptune the cat is bored. He's used to lording it over the other stray cats, but they've all mysteriously vanished.

Where could they be - and how will he find them? Can Effie and her friends reunite before total destruction is wreaked upon the universe?