Tabitha is an extremely deadly biological weapon created presumably by Victoria Galton, Shackleton's adoptive daughter, along with the rest of the co-operative scientists. It is going to be released by Noah Shackleton and the rest of the Co-operative to wipe out the rest of the world population of humans apart from the genetic candidates who could resist Tabitha. The genetic candidates were rounded up and sent to Phoenix (a small town built by the co-operative, for the purpose of keeping the genetic candidates there under the assumption that they had been granted new jobs). After the last person to arrive there, which turned out to be Luke and his Mum, the whole place was locked down and the 100 day countdown was started. Tabitha was supposed to be released on Day Zero although none of the Phoenix citezons realized. The aim for Tabitha was to kill off the rest of the species of humans but not damage any of the wildlife so that the co-operative and the remaining humans could rebuild the world again. it is unknown what format Tabitha is being released as or how it will be released.
Tabitha is mentioned in Arrival by Crazy Bill and the co-operative but it is not mentioned exactly what it is. It is only revealed that Tabitha was a Doomsday weapon.
Tabitha plays a more central role in Contact when Crazy Bill gives pictures to Peter showing the animal testing subjects of Tabitha. The before shots showed the original animal but the after shots the subject was barely recognizable and the only remains were bones and liqufied meat. Crazy Bill then gives Peter a tape with a video showing what happened two of the builders working on Phoenix were exposed to Tabitha. On first looked they vanished but in slow motion their flesh was ripped apart by Tabitha to the point of practically disintegrating. Unfortunately, Cathryn Hawking saw Peter, Jordan, and Luke looking at the video and thinks they're the one that killed them. Tabitha is also shown again when the co-operative finds out about Mathew Reeve helping Luke, Peter and Jordan. Victoria Galton injects Reeve with an unfinished version of Tabitha so that it would work on him. The Trio watch Reeve screaming out in pain when he is administered with Tabitha and he is presumed dead.
It is revealed in Underground that Matthew Reeve is not dead and that the earlier stage of Tabitha only wounded him (This could be because it wasn't supposed to or because he has unnatural healing abilities as a side effect of the fallout). Luke and Jordan are shown a video by Kara of the Vattel Complex around thirty years ago of Luke appearing out of a portal like substance with Peter following him in a fit of rage. Peter then stabs Luke and then goes back though the portal although it is revealed in Fallout that he didn't make it through. Kara then says that Luke then dragged drags himself towards her and said that something called Tobias was to be taken release station to stop Tabitha. Kara then says Luke dies in her arms.
Details on the release station are revealed. It is said by some of the Phoenix security staff that the release station is a building outside the Phoenix Barrier. It is said that there were rumours going around the security force in Phoenix that something called Tobias can stop Tabitha. Jordan's baby brother is born near the end of the book to Jordan's mum with seventeen hours to spare before Tabitha is released. Jordan's mum names the baby Abraham after Jordan and her six year old sister Georgia's Dad. Georgia who can read minds as a side affect of the fallout adamantly claims that the babies name is not Abraham. She says that he tells her it's Tobias. The book ends on a cliff hanger.