Under cover of darkness, Magnus, Will, and Ashley descend into the hold of a bio research vessel moored just outside Old City Harbor. Expecting to meet up with a colleague who has promised an unusual find, they instead come upon a horrible scene of carnage.
Their colleague has been brutally murdered, and it's clear the Sanctuary team is in danger of meeting the same fate. Weapons drawn, they brace themselves against the sounds of ferocious growls emerging from the shadows.
The growls are followed by an attack by a powerful semi-translucent creature, but Magnus sedates the abnormal in its tracks with tranquilizer darts. At her feet, the creature loses its camouflage revealing a fierce predator, capable of great destruction.
With the danger temporarily abated, the team explores the ship's hold and discovers a cage swirling with similar translucent, blurred ripples. As they lean in for a closer look, two adorable, furry creatures suddenly appear, shedding their defensive camouflage.
Back at the Sanctuary lab, the team examines the cute and cuddly little creatures, which Ashley affectionately calls nubbins, to determine what triggers their need to camouflage. The team theorizes that it's a survival tactic to avoid the predator, which is now pacing in its high-security cell.
At the same time, Magnus has been commissioned by last will and testament to autopsy the body of a recently institutionalized elderly gentleman who was convinced he was an abnormal. His granddaughter, Sophie, arrives at the Sanctuary with the body to receive Magnus's assessment along with some assurances that her grandfather was not crazy as everyone believed.
The arrival of the nubbins incites an unexpected rush of romantic feelings among all the Sanctuary's residents. First Henry and Ashley share a moment, followed by Magnus and Will. Then it's Will and Ashley who find themselves alone together in a charged situation, but they're interrupted by a not-so-friendly nubbin which makes a break from its cage.
The next morning, Magnus discovers the nubbins have multiplied significantly, but it doesn't stop there. The team quickly learns that the nubbins have an astounding rate of metabolic growth and an impressive knack for multiplying, not to mention escaping from their cages.
The Sanctuary team locks down the building and nubbin-hunting ensues. The creatures are continuing to breed at an alarming rate and the situation is spinning out of control when they cleverly knock out the Sanctuary's server and com systems, demonstrating that they have a plan of their own.
Realizing that the predator creature must have handled nubbins population control, they decide to turn him loose to do what comes naturally. But they're in for a surprise and an even bigger dilemma when the result is not what they'd hoped.
While Will, Ashley and Henry go on a hunt for more nubbins, as well as a new solution to slow them down, Magnus and Sophie discuss the medical findings and conclusive results of her grandfather's tests. The results lead them to believe that Sophie is not only an abnormal herself, but perhaps their best hope of corralling the nubbins.