A boy in Annie's year from Queslett South, Jack Hyland discovered the power station that everybody snuck out to see in Chapter 19. He says himself that he goes exploring around Gunnerkrigg Court all the time, and he has some technical know-how since he is able to disable the Court's motion detectors and tend to damaged laser cows, as seen during the camping trip chapter. He can be a bit mischievous ( ), and he and Kat seem to hit it off. He looked ready to connect with Kat over their mutual love of technology, but now, in most recent chapters, seems to be more interested in Annie. Most significantly, though, he was the only person besides Antimony and Gamma to get sucked into Zimmy's pseudo-Birmingham when she had a reality-altering episode on the roof. This resulted in Jack becoming a host of one of the more malign denizens of Zimmyngham, which manifests as an etheric white spider.
Jack reappears in "Spring Heeled" several weeks after the camping trip, much more unstable and manic than before. He invites Antimony and Renard to join him on a trip out to the Power Station, and it's revealed that the etheric spider has grown considerably. He can also now see Annie in her enteric form. Jack's instability takes a violent turn when he caves in a guard robot's 'skull', shattering its CPU. It becomes clear that he knew what he was getting into when he starts the Power Station's etheric systems. He also knows about Reynardine and how to bind him, as he hacked into the school database. He then demonstrated that he had gained the ability to fly as he left the Power Station.
Eventually, Zimmy squishes the spider nesting on Jack's head, and that causes him to pass out. Jones mentions that, as he was not in his right mind, Jack would not be punished for his antics. It's been revealed by Jack in a more recent chapter that the spider actually made him more intelligent.
Jack reveals to Annie that he has a crush on Zimmy in Chapter 34 page 28, much to her shock. It is revealed that the white spider was incredibly obsessed with Zimmy, and even when it was killed, part of that emotion was left behind. He only acted as he did with Annie because of her affections for him. In fact, Annie reveals that she didn't really like him either, and only pretended to as part of an elaborate revenge plot. To sum up, neither of them actually loved each other, and the entire romance between them was faked for a lot of confusing reasons.
Much later, in The Torn Sea, we discover Jack has a new girlfriend named Jenny, a cheerful apprentice witch. However, he is still in love with Zimmy, despite his hostile reaction to finding out she was on the boat. Jenny actually knows this perfectly well, and the reasons behind her relationship with him are currently unknown.