With Oona taking the lead this time, the latest adventures follow the Irregulars as they protect New York City and its secret underground world, doing battle along the way with Manhattan's gangsters, rodents, diamond merchants, society figures, and assorted forces of evil. Some of the Irregulars will have to come to terms with deadly secrets from their own pasts, and each of the girls will find her unusual skills and her friendships put to the ultimate test.