Nathan Stark and Allison Blake, annoyed by Eva Thorne's budget cuts, are baffled when they see the costly new lab she has created for Zane Donovan until she explains that corporate sponsorships will cover the set-up and that discoveries will make it profitable.
Jack Carter is visiting Henry when he gets an urgent call from Allison. A scientist has gone missing, From a sealed biosphere. Project Director Derek Bowers explains that 10 volunteers, including the vanished Bob Nobb, have been isolated in an artificially created and maintained underground ecosystem for 11 years.
Derek controls all aspects of the habitat, so, in theory, a malfunction is impossible. Carter, well aware of how much theory may mean in Eureka, insists on entering the habitat to investigate. Although that breaks protocol, Thorne agrees and insists that Allison go with him. Stark is notamused to see his future wife locked up with Carter.
Once inside, Carter and Allison experience the biosphere's atmosphere, realistic right down to gentle rain made from recycled urine. While they interview the inhabitants, Fargo (Neil Grayston) tunes in to the closed-circuit TV feed at Cafe Diem where Eurekans above ground gather to enjoy the show.
It has all the makings of great reality television: a sealed environment, a missing person who may be dead, a nubile woman who may have been involved with him, and several jilted women and jealous men. But, despite having a plethora of murder suspects, Carter quickly realizes that a mutated part of the garden and a reptilian creature hiding there may account for Bob's disappearance.
While Thorne concentrates on turning Eureka into a series of profit centers, the situation in the ecosystem deteriorates. It seems that the repulsive reptile did not eat Bob; it is Bob. Atavism, or devolution is turning Bob into one of our earliest ancestors.
Carter and Allison sedate and examine the man-beast and are amazed to find him radioactive. If radiation is present in the habitat and caused Bob's mutation, it will affect everyone else the same way. Young Teri Wallace, her parents and their fellow scientists are in grave danger. So are Carter and Allison. Worst of all, the only person who can unravel the genetic mystery and reverse the deadly process is Henry Deacon. And Henry is locked in prison with no hope of release.