Tracking the murderer of her fiancee through 19th century London's darkest warrens, Jacky Snapp has disguised herself as a boy—but the disguise fails when, trying to save a girl from the ghost of her jealous husband, Jacky finds that she has made herself visible to the ghosts that cluster around the Thames–

—And one of them is the ghost of her fiancee, who was poisoned and physically transformed by his murderer but unwittingly shot dead by Jacky herself.

Jacky and the girl she rescued, united in the need to banish their pursuing ghosts, learn that their only hope is to flee upriver to the barge known as Nobody's Home—where the exorcist whose name is Nobody charges an intolerable price.