In 1860, Jonas Thunderboom inherits more than a forgotten estate beside the stagnant waters of Thunder Lake. A mysterious obsidian seed arrives with a warning, and beneath the estate's feverish soil lies a secret that refuses to stay buried. When Jonas plants the seed, a monstrous tree begins to grow, feeding on the family's darkest secrets and binding generations to an ancient debt. With Maren at his side, Jonas witnesses the impossible birth of three children-Elin, Soren, and Alrik-whose lives are entwined with the tree's unnatural power. As the children grow, the house twists, clocks defy time, and strange artifacts reveal that every soul leaves something behind. But when Soren vanishes into the lake, the family discovers that the harvest has begun. Some roots reach deeper than blood. Some debts outlive death. And beneath Thunder Lake, something is waiting. The family tree is growing. What will it demand next?