Against Biggie's better judgment, Magnus and Henry are heading into the top-secret government research facility on Abnormals, called SCIU. Biggie worries that they'll get nabbed, and when fears come true, Magnus and Henry are in for a surprise: the director of SCIU is none other than their dear friend Nikola.
Tesla graciously offers them immunity, but Helen senses he's in trouble. As she and Henry are being ushered from the building, a flash of light reveals a giant, tendriled monster that reaches out through an interdimensional rift and devours one of the guards. Helen rushes back to Tesla's office where she learns that the genius inventor has been modifying the rift nodes - the time-traveling device invented by Adam Worth - to create a self-sustaining power supply, and this is allowing the monster to hunt in their physical reality.
Magnus orders Tesla to shut off the node before more lives are lost, but he refuses, proclaiming that the value of his invention is too great. He resists, but eventually concedes, and with both Henry and Tesla on the case, they find a way to seal the rift. Unfortunately, the solution requires a good amount of titanium, and they'll have to cross the monster's path in order to get it.
Biggie and Will have their own "little" problem - a pint-sized Abnormal named Galvo who's full-sized annoying. They want to send him back to Hollow Earth, but they need a bigger load than just one Abnormal to warrant that trip. Galvo volunteers some info on a group of Abnormals who might need a lift, and Will and Biggie hastily arrange a rendezvous. But when the appointed time arrives, the Abnormals are pulverized in an instant by an unseen weapon, and Galvo is nowhere to be found.
At SCIU, the trio makes their way to the metal supply, but on their way, Henry is captured by the snaking tendrils and sucked to the other side of the rift. Helen is furious - not only is Tesla working for her enemy and stealing the government's money to fuel his own experiments in a dangerous bid for fame, but now one of her dearest friends is gone. Still, Magnus insists that they continue with their plan of shutting down the rift to prevent further loss. Tesla's compunction kicks in at the same time that Helen detects Henry's tracking device - he's still alive, and Tesla is determined to travel the rift to get him back.
Tesla uses a remote control to open the rift and free Henry from the creature's nest while Helen keeps the monster distracted in this reality. As the creature closes in on Helen, she must defend herself, and Tesla finds himself dragging a weakened Henry back to their own time just as the beast returns, wounded, to its lair.
Biggie has finally located Galvo and discovers that he vaporized the group of Abnormals because they stood in the way of his race, a people bent on securing the surface for their own use. Will and Biggie capture Galvo, saddened at the loss of so many innocent lives.
Helen and Henry head back to the Sanctuary, clouded over with the fresh betrayal of their complex associate, but the blow is cushioned by an anonymous gift: plans and outlines of every mission and facility of SCIU. Looks like Tesla had one more drop of good in him, after all.