When Mercy Chan washes up on the shores of Hong Kong with no family, no money, and no memories, the only refuge she finds is the infamous, ghost-infested slum of Kowloon Walled City. Since then, she has rebuilt her life, working for the local triad as a ghost talker and dealing with the angry and bitter spirits who haunt the district. The filthy gutters and cramped alleyways of Kowloon have become her home.

But the past Mercy can't remember isn't done with her. An unusually powerful ghost has infested Kowloon's waterways, drowning innocents and threatening the district. It claims to know Mercy—and secrets from her past that are best left forgotten.

As Mercy is drawn into a deadly cat-and-mouse game with this malignant spirit, she begins to realize that the monster she fights within these walls may well be one of her own making.