Eleven-year-old Henry stumbles through a portal and into the clutches of the sinister Mr. Mason. Trapped on a secluded country estate, Henry learns he's not Mason's only prisoner. He must find his place among the other boys, complete mundane chores, and take part in high-stakes games where the loser is killed.
To survive, Henry seeks out unlikely allies: a mysterious deliveryman, a ghost, and creatures from an ominous dimension known as the Yonder. With these allies helping him, Henry sets his sights on fighting back and escaping Mr. Mason for good.
But even if Henry can discover the truth about Mr. Mason's necromantic powers, will he be able to protect his friends? In a world of fragile alliances and ancient grudges, who can Henry really trust?