The Witches isn't easy to summarize because a lot of what happens is rich, detailed description, as opposed to events. Of course, there are some events thrown in there, too, and here they are:
In the introduction, our narrator tells us that witches are real. More importantly, they hate children. Actually, hate isn't a strong enough word, it's more like despise, detest, loathe – to the point of trying to kill children. Unfortunately for the rest of the world, it's hard to tell a witch from a non-witch, because they're really good at disguising themselves. But fear not, Shmoop readers, our narrator is going to give us a few helpful hints on how to recognize these deadly creatures.
Through a dialogue between our narrator and his rather portly grandmother, we learn all about witches: what they look like, how to spot them, what they do to children, the whole shebang. Sure enough, before he can say grobblesquirt, our narrator has a run-in with a witch at his house. He gets away unharmed, but something tells us it's not the last time he'll meet a witch. (By something, we mean the narrator: he tells us himself.)
After a brief Grandmamma-is-sick-and-actually-quite-old scare, our narrator and his grandma decide to take a vacation, and they head for a stay at a giant, beachfront hotel – not too shabby. They also bring along the white mice that Grandmamma bought for her grandson. While training his mice for the circus (naturally), our narrator accidentally finds himself right smack in the middle of the annual meeting of witches. Their leader, The Grand High Witch, and the rest of the witches, take off their disguises and are frighteningly ugly. Our narrator hears these ladies (if we dare call them that) talking about their plan to turn all the children in England into mice using a magical witch formula. He even watches another young boy, Bruno, get transformed into a mouse, right before his very eyes.
Unfortunately, our narrator has the same fate as little Bruno. The witches smell him out and, in the blink of an eye, turn him right into a mouse. Because he's awesome, he's totally unfazed by the whole thing. He goes straight to his grandmother and, being the best grandma ever, she loves him even though he's a mouse. Together, they decide they will get revenge on the mean, old witches.
And do they ever: our narrator sneaks into the room of The Grand High Witch and steals some of the Mouse-Maker formula. After an exciting adventure in the hotel kitchen, he manages to pour the formula into the witches' soup. Back in the dining room, all the witches turn into mice and proceed to be stepped on, kicked, and squashed to death with frying pans. Victory!
Back at home, our narrator really has no complaints about his new life as a mouse. Together with Grandmamma, he decides that defeating the witches of England isn't enough. They need to do something about the rest of the world's witches. They hatch a plan to track down every last witch and turn each one into a mouse. The two adventurers head out on their way, ready for the challenge ahead of them.