Connor's got major beardage. I was surprised, but then I figured it was probably because he and Abby are trapped in the Cretaceous for a while. Same with Abby's wild hair.
I watched the last episode today, so I'll summarize it: After Eve was revealed to be Helen in disguise, she takes Christine Johnson (Lester's government rival who was messing with the ARC all through the third series) hostage and escapes hrough an anomaly she creates with her little future-tech machine. Christine is killed by a future predator.
Abby, Connor, and Danny go through the anomaly at the race track, which they know goes to the same era as the one Helen went through--to the ruined future city that was shown throughout the series--while Becker and Sarah investigate the re-emergence of the anomaly at Christine Johnson's headquarters. They wind up getting trapped in that building by giant future insects for a while, but they manage to escape and return to the race track anomaly, hopeful that the others will return soon.
Abby, Connor, and Danny chase Helen through the future city until they corner her in what turns out to be the ARC, abandoned and dilapidated. She uses some tech there to unlock the artifact's holographic map of anomalies and plot a path to the era she wants: The dawn of mankind. She intends to systematically kill man's ancestors and wipe humanity from history so that Earth and other species have a better chance of surviving into the future. She has to jump through two anomalies to get there--one to the Cretaceous period and the next to the period where man starts evolving. Connor figures out a way to trace her path and open an anomaly for himself and the others to follow her.
Connor, Abby, and Danny roam through the Cretaceous searching for Helen, but they get sidetracked by some velociraptors who try to eat them. They climb a tree and spot Helen, then they knock the raptors out with a stun grenade but Connor gets knocked out, too. Abby insists that Danny follow Helen while she takes care of Connor. Reluctantly, Danny goes.
Danny exits the anomaly to find that Helen has already poisoned a group of hominids, killing them all. He vows to stop her before she can kill the rest but it turns out he doesn't have to. An adult raptor followed them through the anomaly and it knocks Helen off a cliff while she's gloating, killing both of them. Danny wanders around and, much to his relief, finds another group of hominids safely hanging out nearby; mankind has survived Helen's efforts.
Danny sets off back to the anomaly but reaches it just in time to watch it wink out of existence. The series ends with Connor and Abby trapped in the Cretaceous, Danny trapped in the era man began to evolve, and Sarah and Becker in the present but totally unsure of how to get their friends back.