Kai Fukutome (21) lives with his mother, Sachie (53), in Shin-Okubo, Tokyo. After celebrating Sachie’s birthday, he walks his childhood friend Rika (21) home, only for a stranger to attack them. Kai and Rika barely get away. Days later, that same man murders Kai’s best friend, Park Yujun (21). The violence spirals: Rika is left in a coma, and Sachie is killed.

The case cracks open shocking truths: Yujun had been a spy for “Country N,” he has a long-lost twin—Im Jin, a member of the wildly popular K-pop boy group “Littlegang”—and Kai’s estranged father, Im Dohyun (53), is alive in Korea. Overnight, Kai’s fate lurches forward. To avenge his mother and best friend, and to uncover his own roots, he heads to Seoul alone. What awaits him there…?