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.

When a stunning revelation puts Josh and Izzy's lives on the line, Eve and the other survivors desperately search for the young boy who holds the key to saving them; Gavin and Izzy must rely on a stranger if there is any hope to reunite their family.

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.

When a superstorm hits the clearing, a structural collapse puts Marybeth and Lucas' lives in danger.

With time running out before their window home closes, the survivors of the sinkhole hatch a final escape attempt. That plan, however, is put into question when they receive a stark warning from Gavin that their plan will end in disaster and forces Eve to make an impossible choice.

Eve, Levi and the rest of the search party explore a mysterious fort that raises more questions than answers. With the help of a new ally, Gavin and Izzy embark on a dangerous and unauthorized mission to save their family despite government warnings that they could cause unprecedented disaster.

The sight of a crashing plane spreads a wave of unexpected hope through the clearing as Eve and the other survivors search for its fallen pilot. Gavin and Izzy seek help from an unlikely source after the government permanently suspends their mission into the sinkhole.

With the survivors' food supply dwindling, Eve and Ty venture into the forest on a risky hunting expedition only to face unexpected dangers that threaten their survival. As an unlikely rescue mission comes to fruition, Gavin must put his faith – and the fate of his family – in the hands of an old friend with whom he shares a complicated past.

With Josh's life on the line, Eve traverses the dangerous wilderness back to the clearing to save him. Desperate to kickstart a rescue mission, Gavin and Izzy work to prove there are survivors alive inside the sinkhole as government agents track their every move.

When a massive sinkhole opens in Los Angeles, the Harris family is split in two; Eve and her son are sent to a mysterious primeval world; Gavin discovers that the visions that have plagued him for years might hold the key to bringing them home.