When Mimi was little, she stumbled upon a dead body in the dark Missouri woods, and the encounter still haunts her as an adult. Now she unexpectedly confronts her trauma again when she receives a mysterious invitation to spend a weekend on a remote river island.

The Lodge at Demain Island was streetcar magnate Hormel Wurmsman’s dream come true. Pitched as an exclusive getaway for St. Louis’ elite in the years after World War II, the lodge soars atop a Native earthen mound at the confluence of the Mississippi and Missouri Rivers. But by the 1970s, the lodge’s membership has declined precipitously. On its final night of operation, a terminally-ill Hormel reveals a secret to his young grandson, Stefan: in a chamber hidden within the mound rests a perfectly preserved man one thousand years old. By studying the body, Hormel has learned how to extend human life; someday Stefan will join in that pursuit, but he must keep quiet until then.

In the present day, Stefan, now a reclusive tech billionaire, has invested millions renovating the abandoned lodge. He invites six seemingly ordinary people to spend an October weekend there for the soft opening. Mimi, now a zoologist, is joined by an influencer paying her way through college, a Ferguson resident torn between her activism and grad school, an attorney with a disability who represents jailed protesters, a police officer with a military past, and a gregarious fitness instructor to the elderly. None of the six know each other, yet all are enticed by the promise of the luxurious lodge. But after Mimi and another guest discover a deep shared history, they begin to wonder if their invitations were not so random. And when Stefan finally reveals why he invited these specific guests, they are alarmed to find they have no way off the island.