In a near-future Boston swallowed by rising seas, cartographer Imogen Holloway believes she can map her way to safety. As project manager for the Climate Cartography Corps, she's helping build the seawall that will save her city. At home, she applies the same precision to parenting her nonbinary seventeen-year-old, Alix—a photographer who documents the displaced and the dispossessed, and who Imogen is determined to keep close, controlled, and safe. But after Alix is arrested at a refugee settlement and implicated in a resistance attack on the seawall Imogen has staked her career on, her world fractures overnight.

When Imogen’s mother, Elara, is killed at a protest, the only person who can help keep Alix safe is Imogen's estranged father, Lucas—artist, activist, fugitive, and the man she has spent seventeen years trying to forget.

But before Imogen can find him, she must follow the trail he's left behind: a hand-drawn map to a cast of strangers who knew Lucas better than she ever did. As Imogen and Alix pursue him across a fracturing country toward the walled-off Colorado River Basin, old wounds resurface, and new betrayals compound. What was Elara hiding before her death? Who is Lucas, really? And how involved was Alix in the seawall attack?

In a world remade by climate collapse and surveillance-state overreach, The Hidden Heart is a story about the maps we make to find each other—and what we're willing to burn down to keep the people we love safe.