Abby Clover and her friend Spike, the curious boy, found washed ashore after a great storm, are drawn into a world of witches, hidden caverns, fabulous boats, captive children, lost parents, and a quest to find Ice Dust - the source of magical power. With their strange new companions - Captain Starlight, Benbow the giant albatross, and Sir Chadwick Street, flamboyant Master of the Light Witches - they hurtle through perilous seas, face fearsome monsters, and do battle with an enemy, darker and dirtier than they could ever have imagined. With their last sprinkle of Ice Dust gone, the dark fortress of the Night Witch headquarters is a dangerous place to be and it takes more than Abby's new-found talent for becoming invisible to save them.