Granny Weatherwax, Nanny Ogg, and Magrat Garlick, the three witches of Lancre, return home after time abroad to discover that the countryside is being plagued by an outbreak of crop circles. Granny and Nanny suspect that it is the actions of a sinister race of elves seeking to break through into Lancre from their own world. With Magrat's wedding to King Verence looming, the three witches must protect the town from invasion by the Lords and the Ladies

Granny, Nanny, and Magrat, the witches of Lancre, return to their home kingdom after several months abroad. Magrat learns that her married to King Verence, the former Jester, is to take place on Midsummer night. After an argument with Granny, Magrat quits witchcraft and moves into the castle to prepare for her coronation.

Meanwhile, mysterious crop circle have been appearing in the fields around Lancre. Granny knows that this portends an attempt by the wicked race of elf and their sinister Queen to break through into the Discworld at a portal on a nearby hill. The circular portal is surrounded by iron slabs called the Dancers, placed there to keep the elves out. Elves despise iron. Granny learns that while they were away, a group of young girls lead by one Diamanda have been dabbling in witchcraft and holding rituals near the circle. Granny confronts Diamanda, leading to a duel between the two women which Granny wins.

In the aftermath of her defeat, Diamanda visits the stones, where Granny intercepts her and warns her that talking about the elves near the stones allows them to gain greater access to the world. Diamanda runs into the stones and Granny follows. They are met by a party of elves, led by the elf Queen. The Queen orders them killed and Granny and Diamanda flee toward the portal. Diamanda is pierced with an arrow and Granny drags her through the portal, along with a single elf warrior that manages to follow them through. On the other side they are rescued by Nanny, who uses iron to subdue the elf.

With Diamanda healing and confined to the castle, Granny and Nanny are hopeful that the elves will not be able to get a further foothold in the world. But, after the Lancre Morris Men foolishly hold a play near the Dancers, the elves gain a strong enough foothold to invade. The battle begins, and only a coordinated intervention by the three witches leading to a face off between the Queen and Granny and a battle-clad Magrat can save the day.

Granny Weatherwax is seemingly killed in the fight, but she has made special arrangements for that eventuality. Nanny unravels the secret of Granny's fake death and Granny is revived just in time for the wedding and coronation.