 Chiana returns from a Commerce Planet with a cute little creature called a Vorc that is said to be capable of hunting down parasites which may have inadvertently come on board with the crew s supplies. Aeryn thinks Chiana was swindled; the Vorc appears too scatterbrained and unimposing to hunt parasites even if Moya had parasites - and Aeryn doubts Moya does. But Crichton soon encounters a hostile beast eating its way through one of Moya s walls. However, when he tells the others about the sighting, they are reluctant to believe him. Crichton is having an increasingly difficult time coping with more and more frequent flashes of Scorpius. Who knows what else he s hallucinating? When D Argo is attacked by the same hostile beast, everyone realizes that something dangerous and poisonous is on board. This parasite must be caught alive because its toxins are slowly but surely killing D Argo - and Zhaan can t make an antivenin without a fresh sample of the poison. The hunt begins. With the Vorc guiding them, Crichton and Aeryn stalk through the corridors, Crichton fighting off Scorpius flashes all the way. It s then that they discover that the Vorc and the "parasite" beast are one and the same - when the Vorc goes into attack mode and morphs into the beast Crichton and D Argo saw. But capturing the Vorc does nothing to help D Argo. Zhaan is surprised to discover that the Vorc contains no trace of the toxins that are killing the Luxan. Could there indeed be some other creature aboard Moya? To find out, Crichton and Aeryn release the Vorc - which promptly races off, turns into its beastly form, and attacks Rygel! Angry at having misplaced their trust in the Vorc, Crichton and Aeryn track it down in a Cargo Bay, fatally wounding the creature with pulse-pistol fire. But was their trust misplaced? A search of the area reveals a strange alien cocoon containing - Rygel. Crichton and Aeryn realize that the Vorc was leading them to the cocoon to warn them: the injured "Rygel" that Zhaan is tending to is the real parasite - and is about to attack Zhaan!