When Mercy Chan washed up on the shores of Hong Kong with no family, no money, and no memories, she was thrust into the horrors of World War II. She only survived by hiding in Kowloon Walled City, an infamous, ghost-infested slum full of lost and traumatized civilians. Since the end of the war, she has rebuilt her life and found work with the local triad as a ghost-talker, dealing with the angry and bitter spirits who haunt this place. These days, the filthy gutters and cramped alleyways of Kowloon feel like home.

But the past she can't remember won't let her go. An unusually powerful ghost has infested Kowloon's waterways, drowning innocents and threatening the district. Unnervingly, it claims to know Mercy--and her forgotten childhood. 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.

Thirty-three years before, mere days ahead of the Japanese invasion, Sung Siu Yin and her mother flee Hong Kong, intending to hide out on her mother's ancestral island home. It's beautiful, tranquil, and remote. . . but also inhabited by ghosts ever since the entire village drowned in a storm many years ago. Still, it's better than living under occupation.

But as the war drags on and isolation sets in, Siu Yin is increasingly drawn into the island's grim past--a past that may still have a hold on the present. There is a darkness lurking beneath that idyllic ocean, and it has been waiting many years for someone to return.