When the anomaly at Johnson's headquarters reopens, Sarah and Becker head off to check it out. Helen decides the only way to stop the destruction of life on Earth is to stop humans ever evolving and goes back in time to kill Hominids, the very first humans. The rest of the team must stop Helen at all costs. They endure a harrowing journey back through time via several anomalies, battling future predators, raptors and pterasaurs along the way. One of the team also has a life-changing encounter with the earliest humans, Hominids.

今季大結局。Helen深信假若人類從來沒有進化，就是唯一可阻止人類和地球滅亡和的方法，所以她決定去到上新世的非洲，毒害第一代進化的人類始祖。一眾隊員得知Helen的計劃，馬上出發阻止她的行動。就在眾人將要進入異域決口前的一刻，他們手上的偵測器卻失靈了。

與此同時，三隻凶悍的Megopteran透過Johnson總部的決口走了出來，Sarah和Becker逼得前去對付他們。另一方面，Danny、Abby和Connor設法追尋Helen以阻止她的計劃，但Helen卻從異域缺口逃去……