当夏娃和其他幸存者寻找坠落的飞行员时，一架坠毁的飞机的景象在空地上传播了一股意想不到的希望。 在政府永久暂停他们进入天坑的任务后，Gavin 和 Izzy 从一个不太可能的来源寻求帮助。

Eve、Levi 和搜索队的其他成员探索了一个神秘的堡垒，这个堡垒提出的问题多于答案。 在新盟友的帮助下，加文和伊兹开始了一项危险且未经授权的任务，以拯救他们的家人，尽管政府警告他们可能会造成前所未有的灾难。

随着时间在他们家窗户关闭之前所剩无几，天坑的幸存者进行了最后的逃生尝试。 然而，当他们收到加文的严厉警告，他们的计划将以灾难告终并迫使夏娃做出不可能的选择时，该计划受到了质疑。

随着寒冷天气的临近，夏娃、利维和泰回到堡垒，尽管他们在那里有过濒死的经历，但希望能了解公元前 10,000 年。生存技能。 Gavin 试图让 Izzy 免于痛苦，这威胁到了他们的关系

当一个惊人的发现让乔什和伊兹的生命危在旦夕时，伊芙和其他幸存者拼命寻找掌握着拯救他们的钥匙的小男孩。 Gavin 和 Izzy 必须依靠陌生人才能让他们的家人团聚。

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.

Desperate to reunite with her son, Eve follows a lead that brings her face-to-face with a ruthless prehistoric group. Gavin, Izzy and Ella question whether they’re fit to survive in 10,000 BC. Josh and Riley wake up in an unfamiliar time.

After an emotional reunion, Gavin and Eve attempt a daring escape from their unforgiving captors; Lucas leads a dangerous mission to the fort to reclaim the resources his friends so desperately need.

When a fog falls over the Clearing, Eve leads a defense against a group of invaders, only to encounter a threat more dangerous than they’ve faced before. In 1988, Josh and Riley pursue a woman who may hold the key to stopping the impending tidal wave disaster.