After a night of clubbing, teenagers Iliana and Ailith Cestus are set upon by a vampire from an ancient Japanese family. Escaping into the night, Iliana vows vengeance against the creatures ruling the streets of London. A year later, Ailith returns from a soul-searching journey. Now a vampire with mysterious blue skin, Ailith claims to have found inner peace and volunteers to help her sister against the ancient Masakari and her monstrous family. The year has changed Iliana, turning her into a brutal and uncaring hunter. Wary of accepting the help of a vampire - even if it used to be her sister - Iliana is conflicted, since she knows her only chance of defeating Masakari and her brood is to accept Ailith's aid. Working together, they tackle the vampires' human-trafficking operations, although all the while Iliana is keeping a close eye upon her sister. A woman with a foot in both camps, Ailith's loyalties remain ever in question, yet she fears for her sister - Iliana has lost so much, it seems her ultimate aim is not victory against the vampire family but to use them as a means to end her own pain.