TKO: Underground City is the sequal book to the movie TKO: An Human Experiment. It follows the character TKO after she gets caught by Chinese authorities while trying to cross to Taiwan. While in the city, she writes in a diary which is the book. She describes her daily interactions with the gangs, the businesses, the deaths, of the city. In this book, she meets Black Fox, Chan Chan, Red Stripe, and Tsusami.