• The story begins when Mildred and her classmates at Miss Cackle's Academy for Witches prepare for a summer holiday trip to the seaside. • Mildred can’t bear to leave behind her beloved cat, Tabby — but the Academy insists that Tabby is “unsuitable” for a witch. Despite this, Mildred sneaks Tabby along on the trip in secret. • Once at the seaside location (a rundown castle by the cove), Mildred hides Tabby in a boat cabin and tries to keep him secret — but her efforts create a chain of chaos. • At one point, Tabby’s meowing and a mix-up involving another witch’s cat draw suspicion. Things go wrong: the boat drifts out to sea with Tabby and another unconscious witch aboard. • Mildred bravely tries to rescue both her cat and the witch, ends up discovering a mythical treasure chest tied to a rock, and uses its contents to not only help repair the ruined castle — but also earn a reward. • In the end, Mildred gets to keep Tabby, and the adventure ends on a triumphant note: despite all the trouble she caused, she emerges happy, wiser, and — for once — more confident.