Having attained the true keystone to Hollow Earth, Magnus prepares to find her father with the help of Kate, Henry and Will. Since only one vampire shield - designed by Tesla to keep the city from destroying those with Source blood on contact - is available, John and Tesla must stay behind with Adam, who warns them that Helen will never make it through without his help.
Once Helen and her team are inside the main gate, the stone entrance shuts behind them. They discover a detector monitoring the only pathway in. It detects Helen's Source blood and produces shocking laser beams that pursue the four explorers. As Henry and Kate try to avoid death by laser, a tremor rocks the earth and a rock slide separates them from Magnus and Will, who, still pursued by lasers, must keep moving down the hall. They narrowly avoid bumping into an armed guard, and eventually make it to a carved chamber. Their relief at making progress is interrupted by a venom-spitting basilisk. It seems there's no way out of his lair, but then a family of three mysteriously appears. Will and Helen try to save them, only to realize that they're holograms. Their flesh-and-blood counterparts appear and usher them to safety, feeding them a strange plant called "rashi" to help them regain strength and telling them of their lives: They are farmers of the highly nutritious fungus that grows underground, and they live outside of the city - called Praxis - not by choice, but by law. They agree to lead Helen and Will close to the city, but warn them that no one may enter without clearance.
The tracking device John gave to Helen was destroyed in the rock slide, making him and Tesla anxious for Helen's safety. Left with no other options, they cajole Adam into releasing his Hyde persona and helping them make sure Helen is safe. Almost too easily, he agrees, and finds a way to hook up the probe to his own brain - sent by him when he attacked Will months ago - to gain the data about the city. Tesla then translates the computer code produced, and Adam tells them how and where to go. Leaving Tesla behind once again, John and Adam teleport to Hollow Earth, with Adam practically skipping down the cavern halls. But in a wink, Adam has allowed Hyde back in, and his minions - the same creatures that attacked Will - have now attacked and overpowered the duped John, whose teleportation has been disabled by the caverns' high concentration of magnetic lodestone.
Kate and Henry follow a system of running water, hoping it will lead them to the city, but they're soon apprehended by silent henchmen and thrown in jail. The only upside to this is that they share a cell with Will and Magnus, who were detected when they stepped into the city's highly advanced mass transit system. Soon, the quartet is taken to meet the ruler of Praxis, but any hopes of a warm welcome are dashed when she coldly and fixedly informs them that the penalty for trespass is death. Soon, the "surface dwellers" find themselves suspended in electromagnetic crucifixes of sorts. Though they plead that they are only there to help Gregory Magnus, the city's ruler orders their execution, and a deadly jolt of electricity runs them through.