Stella Lindy is supposed to be soaking up the sunshine with her bridesmaids on a bachelorette cruise to Hawaii. But when she hits the wrong button on the elevator, the glamorous luxury of the modern ship is replaced with the Missouri River steamboat Arabia filled with strangers—and a mysterious doctor informs her it is 1856.

Communicating through an antique mailbox, her friends on the cruise try to guide her back home before the steamboat sinks, but Stella finds herself caught in a tangled web between pro-slavery Border Ruffians and anti-slavery Jayhawkers. Standing up for what's right in the face of peril and uncertainty might mean never making it home.