In November 1982, a Chevy Blazer was found running along Interstate 80 near Elk Mountain, Wyoming. The doors were open. A single set of footprints led north into the prairie.

The vehicle belonged to 35-year-old Don Kemp, a former New York advertising executive who had set out west to write a book. Days later, a storm shut down the search.

Months after Don was believed to have died, a turn in the case raised a startling possibility: that he might still be alive.