Emily Snow is twelve years old, supporting herself and her younger brother on the streets of Victorian England by selling watercress. One early winter morning on her way to buy supplies, she encounters a piskie--a small but very sarcastic fey creature that has been cornered by a group of the Black Sidhe, piskies from an opposing clan. She rescues him and unknowingly becomes involved in a war between the Seelie and the Unseelie, two opposing factions of fairies that have been battling each other throughout the long centuries of human history, with London--and England itself--as the ultimate prize.

When the Invisible Order--a centuries-old secret society of humans that has protected mankind from the fey's interference--gets involved, things really start to get complicated.

Now she is the central figure in this ancient war that could permanently change Earth. With no one to trust, Emily must rely on her own instincts and guile to make the right choices that could save her family and all of mankind.