Thirteen-year-old Clementine Merlyn lives with her mom, her aunts, and her cousin Mirabelle at Number 15 Pendragon Road. The Merlyns are a family of witches, but because of an ancient falling out with the other branch of the family, the Morgans, they only have powers for a single month of the year: October.

And this October may be the one that Clemmie gets her magic. It should be exciting, except that magic is the reason that Mirabelle never talks to her anymore, Aunt Flissie leaves at the end of every September and doesn't come back until November, and Aunt Temmie...well, is long gone. And the Merlyn bad luck takes an even worse turn this year. After a disastrous attempt by the aunts to recover their lost magic, 15 Pendragon Road is visited by the creepy and cold Morgans.

In the wake of the ensuing battle, Clemmie and Mirabelle are left on their own. With no other choice, the cousins must bond together and summon their courage and magic to solve the mystery of what happened between the first Merlyn and Morgan all those centuries ago if they'll have any hope of ending this feud and getting their family back.