Nathan Mallstrom, during a routine shift deep in Clean El Mines, finds The Teather, an ancient artifact believed to be the original link between this Earth and Dark Earth. When The Teather transfers its power to him, Nathan finds himself teleported to Dark World and back again, bringing unwanted demonic visitors with him. Summer Vale and Bulo arrive to save the day, but are left with more questions than answers. They try to explain to Nathan exactly how his new powers will affect his life and the responsibility they bring.

On the run from demons Nacelle and Rosemary, Nathan heads into town to seek his sisters help. Ending up cornered by Rosemary, Nathan is aided by Davidath who is injured in the confrontation. While Summer battles Rosemary, Davidath is brought to Gwen's Clinic to try to save his life where he reveals that he has something for Summer - The Trankartak, an ancient black sword that steals the life force of it's vicitms and grants it to it's wielder. The weapon arrives just in time as Summer is put to the test.

Summer returns to Paris to meet her with her contact while Nathan and Bulo handle things in Nickel City. After placing a protective shield around Gwen's Clinic, Nathan finds out he may need some help with his new powers. Bulo suggests a trip to see an old friend who might be able to help: Weeber. When removing The Tether doesn't work, Weeber thinks of a way for Nathan to control it instead, and not a second too late as the team has to go on a hunt without Summer.

Sckraab, ruler of Dark Earth, arrives to put into place the final pieces he needs to enact his plan. He desires to bring his armies over using The Teather to conquer and rule both worlds. His true evil Is revealed as he shows exactly how far he is willing to go to make this a reality. Summer discovers her true origin and comes to terms with the role she must play in stopping Sckraab and his minions.

The team is still dealing with the hard hit Sckraab just dealt them, but they pull together to devise a plan to bring all of this to an end. Summe rhas a final showdown with Rosemary, and Nathan visits Nacelle and Sckraab at the mine for the battle of a lifetime. When Nathan is captured, Aramas reveals the "real plan" to Summer. She must now make a choice to decide the fate of two worlds and nothing will ever be the same again.