With cold weather approaching, Eve, Levi and Ty return to the mysterious fort, despite their near-death experience, hoping to learn 10,000 B.C. survival skills. Gavin's attempts to spare Izzy pain threaten to do their relationship more harm than good.

With news of one last sinkhole opening, Gavin, Izzy and Dr. Nathan race to Seattle to launch a final rescue effort before it's too late; Eve embarks on a perilous journey to send a young boy though a portal in order to save her family.