Will wakes in a powerful state of disorientation and rushes to the staff meeting, for which he's already late. But when he arrives, Henry notices something scaly growing on Will's face, and Magnus rushes Will to the lab to start testing and discovers that a spore is altering Will's DNA. After an exhaustive search in the Abnormal database yields no clues, Magnus realizes that the thing mutating Will must be from another world, the most likely world being Hollow Earth.
Magnus instructs Henry to contact Ranna, their liaison in Hollow Earth, to see what she knows, but Ranna replies that there is no cure. They must terminate Will immediately. This, of course, is not an option, so despite Will's worsening condition - he's looking more like a lizard every day and is now able to climb walls thanks to the scaly outgrowth on his skin - she continues to hunt for a cure.
The perks of being able to climb a wall are dwarfed by the dangerous aggression Will is starting to display, so the team subdues him and locks him up in one of the medical observation cells. In a flash of insight, Magnus revisits the response from Ranna, noting that it had some distortion attached to it. Henry slows the transmission to the point where the team is able to hear a rhythm in it, and they soon deduce that Ranna sent them a message in Morse code: Gooban.
Gooban? As they research Hollow Earth history, they discover that Gooban is the name of a botanist who developed a cure for the siege Will is enduring, and it involves a particular kind of mushroom that bears his name. They concoct the solution needed to combat the alien spore, and head to collect Will.
But when they get to his cell, he has almost fully transformed. He attacks Henry and Kate and flees the Sanctuary. The team assemble with doses of the cure, but everyone is prepared to use lethal force, should they need to.
Reports of sightings of a strange lizard creature have been coming in to the Sanctuary network, so the team head there. Magnus slips down an alleyway, following sounds of disturbance, and soon finds herself in hand to hand combat with the creature that Will has become. He knocks her tranquilizer from her hands, and she reaches for her firearm, but hesitates a moment too long, allowing Will time to knock her to the ground. As he's bounding for the final stroke, she grabs a syringe of the curative and stabs him in the neck.
Several days later, Will revives in the Sanctuary, alive, shaken...and just a little sad that his cool superpowers are missing.