Life will never be the same for twelve-year-old Ananka Fishbein after she ventures into a sinkhole near her New York City apartment.

Not only does she discover the mysterious Second City beneath Manhattan's bustling streets, she meets the mysterious Kiki Strike, a black-clad, Vespa-riding, cafe-au-lait-drinking girl superspy.

Ananka joins Kiki as she recruits four delinquent Girl Scouts into an elite squad - the Irregulars - to explore and map the Second City.

But someone else is after the secrets of the underground labyrinth and when Kiki's loyalty is questioned, Ananka will have to take matters into her own hands.