Tessa Miyata has never fit in. When she and her two sisters are told they will be staying with their grandparents in Japan, Tessa is thrilled. A summer in Japan could be her chance to go on an adventure worthy of impressing her classmates back home.

Her hopes are quickly dashed when she realizes her sisters are old enough to go into Tokyo, while she can’t even go to the corner store by herself. Plus, her grandparents want her to stay home with the neighbor kid, thirteen-year-old Jin Uehara, who’s made it clear he’s too cool to spend time with a weirdo like her.

When Tessa is finally allowed to go to Tokyo, it’s only to join her grandpa’s retiree aerobic class with none other than Jin. Their disastrous forced hangout comes crashing to a halt when Tessa and Jin break the Miyata family’s precious heirloom—accidentally releasing the malicious samurai god Taira Masakado and discovering a hidden part of the city where gods and mythological creatures walk among humans—including their new companion, a mythical nine-tailed fox who may be more trouble than he is help.

Tessa and Jin must now work together to stop Taira Masakado before he traps them—and the rest of Tokyo—under his command, forever.