Ghosts of the River Thames — Amy Cross

When she travels to London in search of her sister, Katie quickly finds herself drawn into the city's dark underbelly. Soon she's living in a strange, derelict old house, where a strange man keeps watch over a group of undead girls. Meanwhile, her sister Rachel is trapped in a nightmare of her own. Relentlessly reliving her own murder over and over again, Rachel sets out to discover the truth about how she really died. Before long, however, she realizes that she's caught up in a much greater, much more dangerous plot that threatens not only London, but the whole world. Ghosts of the River Thames is the first book in the Robinson Chronicles series, about a dark forces awakening beneath the streets of one of the world's oldest cities.