Evie Swan has a great life, an amazing job, a beautiful child, and a big problem: she is fat. Evie is desperate to lose weight, but every diet she's tried has failed.

One day Evie meets a mysterious stranger who gives her a magic mirror. The mirror is a portal to an alternate universe where Evie's life is the same in every way except one. On the other side of the mirror, she has the skinny body of her dreams.

But the spell comes with conditions. Evie has three chances to use the mirror, and one choice to make. She must decide whether to be fat or to be thin.

The decision about which body to choose seems like a no-brainer. But Evie's adventures through the mirror make her choice less straightforward than expected.