At night, the security team spot what appears to be a Sixer out in the perimeter so they go and investigate. It turns out to be a terrified young girl, a la, the runaway.
The little girl, threatened by getting a jag, goes AWOL and hides under the table at the infirmary. Of course it’s Liz who comes to the rescue and forces everyone out of the facility. She’s able to lure her out and Liz discovers that the girl’s parents are dead and that she is a part of the Sixer team. Taylor brings the runaway food and she confesses he is named a “bad man” at the Sixer clan and she left because she wasn’t getting enough nutrients so she is heading to her gran. Unfortunately, gran is 85 million years in the future, so don’t think she’ll be seeing her anytime soon!
Taylor can vividly remember the girl before she left and announces her to be Leah Marcos and she has a younger brother, Sam. Liz pipes in that Leah is healthy, but Jim is able to stop her from bombing out and the two explain that the portal only leads to Terra Nova, you can’t go back again. Now Leah is really in trouble as she doesn’t want to stay with Taylor and she can’t go back to the Sixer’s.
Commander Nathaniel, like always, opens up to Jim and unveils his new plan to use Leah to find out more about the Sixer’s, but first they need to gain her trust. Liz pleads for Jim to take Leah into their house as she has nowhere else to live and he agrees.
Washington and another security guard go in search of Leah’s missing bag that she left in the jungle. However, it’s been booby-trapped and when they find it Sixer’s appear out of the bushes and start attacking them. The security guard is taken almost instantly, but Washington puts up one hell of a fight, until Mira comes along and bashes Washington’s head with her gun.
At the Shannon’s household, the family do their best to welcome Leah. Maddy dresses her up in a cute yellow outfit, which Leah doesn’t like, Zoe show’s her a drawing of the family, without Leah in it, and Josh gets forced to look after the youngsters as everyone else has more important matters to attend to.
Maddy’s first day working with her mum is quite horrific, with their first patient being a man whose arm has been ripped apart. Commander Nathaniel asks Jim if it is too early to start asking Leah questions about the Sixter’s, however, they don’t get the chance to talk much as the Sixer’s arrive and Taylor allows the gate to be open: they’ve come for Leah. Nathaniel takes full command of the situation, telling Mira to let his people go and Leah can decide herself if she wants to go back with the Sixer’s or not. Washington and the other security guard are freed and Jim brings Leah out and gives her some good advice to tell the truth. Leah admits to Mira that she runaway and that she wants to stay with Taylor. Before they leave Taylor warns Mira that if the Sixer’s come to their gates and threaten the camp again he will go to war!
Taylor tells Jim that he wants to find out who in camp is informing the Sixer’s as he or she must have told them of Leah’s arrival. He’s also able to bring Leah on side and asks her, once she’s settled in, to look at some maps to see where the Sixer’s camp is. Jim has been doing his little task for Taylor and brings back a list of names that could be the Sixer’s inside man. One name, Robert Stanley, catches Taylor’s eye as he came through on the sixth pilgrimage, like the Sixer’s, but decided to stay in Terra Nova camp. When they speak to Rob, Malcolm appears and explains there’s no way it can be his friend. Taylor and Jim leave, but Taylor warns Malcolm that he needs to drop his growing ego. Maddy and Liz take Leah to her first day of school, but when they walk away reminiscing on Maddy’s first day, Leah does what the title suggests and runs away.
A residence household has been broken into with something being stolen from an unknown compartment underneath the ground. Washington informs Jim that this was Mira’s house. Jim catches Leah trying to escape through the fence and asks what it was she had stolen. Leah tries to bolt but Washington and her crew appear, and make Leah hand over her bag.
At Nathaniel’s office, he explains that everything has been a set up. Mira knew Taylor would allow Leah into their camp and the Sixer’s trying to bring the girl back threw him off the sent that this was a trap. In the bag there is a strange container and Taylor commands Leah to be brought in to help them open it. Leah is unable to do so and when Jim starts to get angry she admits that she doesn’t know what’s in it and she had to lie because Mira was going to hurt Sam if she didn’t bring back the container. Taylor doesn’t seem convinced and he won’t do anything to help Sam until he finds out what is in the container.
Taylor tells Jim to go home, he believes Leah’s story, but Taylor won’t allow him to do anything about it as it could end up being another ambush if they send men out there. Back at the Shannon’s, Maddy leaves and Liz explains she had a bad day at the infirmary, Josh escapes back to his room and Liz confesses she doesn’t like people taking advantage of her family. Josh comes back after discovering a note left from Leah saying: “Sorry I had to” with a sad face. Leah was telling the truth!
On a lighter note, Reynolds and Maddy are finally dating after the soldier really awkwardly asked her out! Jim goes alone to see if he can find Mira and co and save Sam, however, he ends up stepping on a booby-trap and the Sixer’s rescue him before he becomes Dino food, and they take him to their camp which is high up in a canopy. Mira enquiries Jim and tells him that Sam was never in danger; he was just a scapegoat to force Leah into action. She explains that Taylor has angered a lot of people back in the future who want him dead and that Terra Nova isn’t about starting again, although it is unclear what its purpose then is. Mira tells Jim that he should move over to their side to protect his family as at some point Taylor will be exterminated. However, it’s not Mira being mean of her own accord; she confesses she is doing this for her daughter, Sienna, who is back in the future. If she can get rid of Taylor she will be reunited with her Sienna. Jim asks who her boss his, but she ignores him and lets him leave along with Sam.
After reuniting Leah with Sam, Jim goes to talk to Taylor and explains that Mira let them both go to prove a point: they’re not the bad ones. However, Jim doesn’t believe them because they bust his ribs, fair point. Jim keeps his trap shut about Mira’s intentions when Taylor asks if Mira mentioned anything that he doesn’t know. Liz patches up her husband and tells him that she let Maddy leave her training as it wasn’t exactly what she thought the work of a doctor would be, e.g. it was too gory. Someone wants to adopt Leah, and hopefully the newly arrived Sam too, and the little runaway really respects Jim and his family from bringing her younger brother back to her safely. Malcolm still is unable to open the container and he stores it in a safe place. Hopefully they will unlock its secrets before the Sixer’s come searching for it again!