Strange things are happening in Lily Ivory's San Francisco. First, she finds a vintage mermaid costume which dates from the 1939 San Francisco's Treasure Island World's Fair - and which gives off distinctly peculiar vibrations. Next, she stumbles upon a dead man in the office of her predecessor, and as the community's new leader, she feels compelled to track down the culprit. Just when Lily thinks things can't get any stranger, a man appears claiming to be her half-brother, spouting ideas about the mystical prophecy involving San Francisco and their family...

When the dead man is linked to the mysterious mermaid costume, and then yet another victim is found on Treasure Island, Lily uncovers ties between the long-ago World's fair and the current murders, and begins to wonder whether the killer might be hiding in plain sight. But unless Lily can figure everything out in time, there may be yet another body floating in San Francisco Bay.