A chopper focuses a searchlight on a cargo ship in open water. Will, Ashley and Helen Magnus enter the shipâ€™s dark hold. Eric has promised them something that theyâ€™d â€œnever seen beforeâ€; however, Eric is now dead. He and his team have been ripped apart and â€œhalf-devouredâ€. Empty transport cages lay crushed and pried open. Ashley discovers two quasi-invisible furry creatures in an undamaged cage. Then a large, quasi-invisible beast begins growling at them. Magnus orders â€œtranquilizer rounds onlyâ€. Ashley wants to kill it but her mom says â€œEric paid with his life to bring this creature back. We owe it to him to preserve itâ€. They subdue the beast.
Safely back in the Sanctuaryâ€™s lab, the team discusses the new creatures. Ashley has dubbed the two small â€œadorableâ€ ones Nubbins. However, wounds on the bodies of the crew show traces of both creatures. Henry, sneezing uncontrollably, turns out to be allergic to the small creatures. The opening notes of increased sexual tension sound as Ashley is talking about her nubbins and Henry is obviously thinking of something else. He looks pained and forlorn when Ashley asks â€œDonâ€™t you just want to squeeze them?â€ Meanwhile, a young woman named Sophie has arrived at the Sanctuary with the body of her grandfather - who wanted Dr. Magnus to perform an autopsy on him. He had lived out his last years at a sanitarium believing that he was an abnormal. Somehow he had known about the Sanctuary. Will attempts to comfort a painfully defensive Sophie but is evasive when Sophie wants to know what goes on at the Sanctuary.
Dr. Magnus is explaining to Will how equatorial cultures considered Nubbins both harbingers of fertility and â€˜portents of discordâ€™ if they vanished when he draws closer. Both appear â€˜distractedâ€™ and perhaps aroused. The team discovers that the female Nubbin has given birth - there are now 14 of them. Ashley is increasingly drawn to the little Tribble-like creatures. The predator creature, on the other hand, is becoming agitated - as is Sophie when she learns that she might share her grandfatherâ€™s â€˜anomaliesâ€™. Dr. Magnus has Will give her a tour of the Sanctuary so that she might better understand. Sophie is surprised at what she sees but takes it well. Her â€˜extra-sensoryâ€™ perceptions seem to be increasing, making her weak and dizzy at times. Ashley is in her room cuddling with a Nubbin when Will comes to check on her. The Nubbin reacts defensively and urinates on Dr. Zimmerman. Ashley unbuttons his shirt and cleans his chest. Both are oddly and obviously aroused. They almost kiss but are startled when the gage door breaks and the Nubbin is gone. A Nubbin is next seen eating away at the metal grating and piping beneath their habitat. They have escaped.
Team Magnus begins a search with Ashley still protective of the little â€˜furballsâ€™. All the food stores have been emptied. They go â€˜floor by floorâ€™ with flashlights, snares and tranquilizers - to no avail. One of the creatures gets scared and bites Henry. When told that he may need a complete series of painful rabies shots Henry argues with Ashley : â€œHey, listen, I know youâ€™re all about saving the whales and everything, but these guys just happen to be a pack of vicious, over-sexed, hyperthyroid invisi-rodentsâ€. Rodents who now may number at least 70. Ashley is chastised by her mother for her lack of judgment. The futile Nubbin search continues as Dr. Magnus examines Sophie, who is worried when she learns that she has the same extra â€˜tissue structureâ€™ in her brain that her grandfather had. When Dr. Magnus reveals to Will that the Nubbins emitted powerful pheromones, he is embarrassed and denies noticing the â€˜arousal effectâ€™. â€œAwkwardâ€, he says. â€œPoor thingâ€, replies Dr. Magnus.
The computers begin crashing because the Nubbins are now chewing their way through the infrastructure systems. Dr. Magnus considers releasing the predator beast to curtail the Nubbin explosion. She plans to implant a tracker/controller in the creature. Sophie senses that the beast is frightening the Nubbins. Despite Willâ€™s attempts at comfort giving, her â€˜giftâ€™ makes her feel like a â€˜freakâ€™ who belongs in a sideshow. Henry gleefully uses a giant vacuum to capture a Nubbin. Then the â€˜predatorâ€™ is released and begins herding and killing the fleeing Nubbins. The tracker indicates that the â€˜beastâ€™ has stopped just outside the library as power fails and the lights go out. Will and Helen investigate and find blood and chewed Nubbin all over the place. Then, in the library, they find the bare carcass of the now dead beast. â€œLooks like our predator just became preyâ€, Will quips. Dr. Magnus opines that they may be next.
Will remembers the hold of the cargo vessel was set to 50 degrees and Dr. Magnus conjectures it may have been an attempt to slow the Nubbins metabolism. The team round up fire extinguishers as the frightened Nubbins begin to send out warning cries. Dr. Magnus and Henry determine that the Nubbin distress call is at the ultrasonic sound level of 21.5 kilohertz. They set up sound emitters to herd the creatures so they can be â€˜chilledâ€™ by the fire extinguishers. Once â€˜asleepâ€™, the Nubbins are returned to their now chilled habitat where they can â€œlive out their days in relative peaceâ€. Sophie, coming to terms with her â€˜giftâ€™, prepares to leave the Sanctuary.