Nancy Springer

"After a mysterious group of anarchists abducts Mycroft, Enola investigates his disappearance in hopes of rescuing him and of getting back something precious he took from her. With the help of Lord Tewkesbury and a young boy on the streets named Shag, she uncovers the truth behind her brother's abductions and unravels a web of mystery that takes her deep into the London underground as she tries to foil the anarchists' nefarious plot!"--