When sixteen year old Tessa Gray arrives by steamship in London to meet her brother, she is met instead by two creepy women from a dark, gloomy mansion. Only when they show her a letter handwritten by her brother does she agree to accompany them to their lair. Tessa becomes their prisoner. They teach her to use her unknown powers to shape shift. Unbeknowst to Tessa, she was born with powers to become anyone or anything. This quality, or gift, makes her highly valuable to the mysterious and terrible Magister. The Dark Sisters tell Tessa that they are to deliver her to this evil man, but Tessa is grabbed and spirited away by two young men who tell her they are Shadowhunters, trained warriors with special gifts who fight Downworlders like vampires and warlocks to save humans.
Tessa yearns to find her brother and fears for his life. The Shadowhunters agree to help her find him, if she will use her shapeshifting powers to help them infiltrate a vampire clan. Tessa finds herself torn--does she love the dark and brooding Shadowhunter who saved her from the Sisters? Or does she truly hate him?