The Harrises return to 10,000 BC, determined to upload a virus that will stop all sinkholes, despite knowing that this will mean they will never get home again. An unlikely leader rallies the Clearing to face an oncoming prehistoric threat.

A ruthless enemy holds the Clearing captive, threatening to kill a beloved Survivor if their demands for an unexpected item aren't met. Gavin and Sam lead the rescue attempt, aided by an old friend whose return holds more questions than answers.