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.

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.

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.

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.

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.

When a chaotic superstorm hits the clearing, a structural collapse puts Marybeth and Lucas' lives in danger. Eve, still at odds with everyone, tries to make amends by leading the effort to dig them out. Gavin embarks on a journey into his past.

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

Amikor egy megdöbbentő felfedezés Josh és Izzy életét veszélyezteti, Eve és a többi túlélő kétségbeesetten keresi a fiatal fiút, aki a megmentésük kulcsát rejti magában. Gavinnek és Izzy-nek egy idegenre kell támaszkodnia, ha van remény a családjuk újraegyesítésére.

Egy utolsó víznyelőnyílás megnyílásának hírére Gavin, Izzy és Dr. Nathan Seattle-be száguld, hogy elindítsák az utolsó mentőakciót, mielőtt túl késő lenne. Eve veszélyes útra indul, hogy egy kisfiút küldjön át egy portálon, hogy megmentse a családját.