Twelve-year-old Ananka Fishbein has a life she compares to “flavorless mush.” Then one morning she glances out her bedroom window and sees that an enormous sinkhole has swallowed a small park near her Manhattan home.

Ananka sets out to investigate and discovers the entrance to a vast network of tunnels once known as the Shadow City. One hundred and fifty years ago, it was home to New York’s thriving criminal community. Now the tunnels lie abandoned and (almost) completely forgotten.  

Soon after her discovery, Ananaka meets the mysterious Kiki Strike. A tiny, white-haired girl who claims she’d like to be “dangerous,” Kiki has not only visited the Shadow City, she also knows things about Ananka that she has no business knowing.

Throwing caution to the wind, Ananka joins forces with Kiki Strike, and together they assemble the Irregulars—a band of six delinquent Girl Scouts with talents that range from picking locks to the art of disguise.

As the Irregulars use their unusual skills to explore the Shadow City, they must confront skeletons, man-eating rats, exiled royalty and devious criminals. They must also unearth plenty of dark and deadly secrets—about each other and their bizarre young leader.