When the mummified remains of numerous victims are found in the walls of an elderly couple's remote South Carolina home, Rossi, JJ, and Simmons are dispatched to track down a trail of clues that date back over 20 years. The hunt becomes urgent after BAU learns the killer has a specific ritual of when to strike, and like clockwork another person goes missing. Also, Rossi reconnects with his ex-wife, Krystall.