Cordelia Carstairs, a Shadowhunter trained to battle demons, travels with her brother to London where they reconnect with childhood friends but soon must face devastating demon attacks in the quarantined city.

Edwardian London, a time of electric lights and long shadows, with demons waiting in the dark. For years there has been peace in the Shadowhunter world. James and Lucie Herondale, children of the famous Will and Tessa, have grown up in an idyll with their loving friends and family, listening to stories of good defeating evil and love conquering all. But everything changes when the Blackthorn and Carstairs families come to London, and so does a remorseless and inescapable plague. James Herondale longs for a great love, and thinks he has found it in the beautiful, mysterious Grace Blackthorn. Cordelia Carstairs is desperate to become a hero, save her family from ruin, and keep her secret love for James hidden. When disaster strikes the Shadowhunters, James, Cordelia and their friends are plunged into a wild adventure which will reveal dark and incredible powers, and the true cruel price of being a hero and falling in love.