Michael is still keen to find out the truth about the spaceship that crashed but Max is content to leave it. At the Air Force base, scientists are studying the ship. They find a compartment contains a baby, shortly before something attacks the lab, killing everyone in sight, and takes the child. Later, Carlson and Colonel Thompson review security footage of the incident, including the culprit.
Max and Liz are getting intimate when they get a call from Diane summoning Max for dinner. Max tells Liz to meet him at Michael's later. Isabel and Jesse get the same summons. Jim and Kyle arrive home and find the house has been trashed. They hear an intruder who blows a hole in the wall in order to escape.
Philip and Diane show Max, Isabel and Jesse the video of Isabel using her powers. Their demands for an explanation are cut short when they hear someone in the house. Max finds an injured Tess with the baby, who she hands to him before collapsing. When she comes round, Max questions her. She named the baby Zan, which she considers to be Max's real name. Kivar rejected him so she escaped: Her ship crashed after the encounter with Griffin's plane. Max is horrified that she killed 15-20 people in the name of protecting Zan. Tess helps him that she and Zan are linked, so he can't kill her without killing his son.
The Air Force track Tess to the Valenti house. Jim feigns ignorance when shown a photo of her. Kyle slips away and phones Jesse, who lets Max, Isabel and Tess go. In desperation, Isabel admits to their parents that she, Max and Zan are all aliens and "bad people" are after the baby. Carlson comes to the door. Philip stalls him by demanding to see a warrant; Carlson pushes past him but Max and Tess slip away with Zan. Carlson's people search the house and take the video of Isabel using her powers.
Max takes Tess and Zan to Michael and explains why they can't hurt her. Liz turns up and the sight of Tess triggers her powers, which she blasts Tess with. Max steps in and Liz leaves, angry. Kyle also arrives but isn't in a mood to forgive Tess either. Liz complains to Maria about Tess being back but won't let Maria tell the military, who are scouring the streets and setting up road blocks on the pretext of looking for stolen explosives.
Max and Michael attempt to drive Tess and Zan through a roadblock with Tess using a mind warp to hide them but she is unable to main the illusion and they have to flee back the way they came. Everyone reconvenes at Jesse and Isabel's house, where Tess tells them to save Zan over her. She admits she made up the link between them and Zan is fully human, having only received that DNA from her and Max. However, the only way to stop the Air Force chasing them is if they catch Tess. They vote on whether or not to hand Tess over to them: Michael, Maria and Isabel vote yes while Max, Jim and Kyle vote no. With Jesse abstaining, Liz has the casting vote and votes no.
During the night, Tess wakes Liz and has her drive her to the hillside overlooking the base. Tess tells Liz that every time Max kissed her she could tell from the flashes she got that he really loved Liz, saying she wants to do one good thing with her life. Liz realises Tess isn't let herself get locked in the White Room and Tess confirms it. She burns a hole in the fence and advances towards the base. Liz hears shouts and gunfire, then the base explodes.
One week later, Max tells Philip, now accepting of the truth, that someone will always be after him and he can't keep Zan safe without giving him up. Philip says he knows someone in New York who can arrange an adoption. Some time later, Liz hugs Max as Philip and Diane take Zan to his new family.
- This is the penultimate episode of Roswell.