On the series premiere, the Harris family is split up when a huge sinkhole opens in Los Angeles; Eve and her son end up in a primeval world.
Eve navigates the dangerous wilderness in order to save Josh; Gavin and Izzy work to prove survivors are alive inside the sinkhole.
Eve and Ty venture into the forest on a risky hunting expedition; Gavin must put his faith in the hands of an old friend.
With cold weather approaching, Eve, Levi and Ty return to the fort, hoping to learn 10,000 B.C. survival skills.
On the season finale, there’s news of one last sinkhole opening and a race to Seattle to launch a final rescue effort before it's too late.