Novaline Cromwell Warner and her sister Natasha Jules Warner were once inseparable, sharing an unbreakable bond of trust and confidences. But a horrific accident in their youth irrevocably shattered that closeness. When Nova was just a little girl, her family was forced to flee their home in Sydney and relocate to the United States after a deeply traumatic experience involving Natasha and her friends venturing into the long-abandoned tunnel system beneath the city. Their ill-fated expedition, meant to shed light on the plight of the homeless living underground, turned into a nightmarish ordeal. One member of the group perished before they could escape, another died shortly after clawing their way back to the surface, their body ravaged by mysterious forces. The only two survivors, Natasha and her boyfriend Steve, emerged deeply haunted, the secrets of what unfolded in those subterranean depths forever locked behind their lips. A year later, in 2011, their found footage finally surfaced online, igniting wild conspiracy theories about what the government might be covering up in the tunnels. At first, Nova became obsessed with unraveling the truth her sister still refused to share. But as the footage and accounts circulated, Steve vanished without a trace after going back down, his fate unknown. Now, unable to move on from the nagging doubts, Nova has assembled a small team of urban-explorers to plunge into the dank, claustrophobic and pitch black confines underneath Sydney, Australia, from which Natasha barely escaped with her life over a decade ago. Nova has spent years training to be a silent, unseen warrior, honing herself for the dangers that may lurk in the shadows. But her brazen quest to confront the deadly secrets head-on will force Nova to truly put her skills to the ultimate test of survival. As they descend into the inky subterranean maze, Nova's team realizes too late that they are not alone. Something ancient and malevolent still dwells in these abandoned tunnels, a presence that seems to defy all logic and human understanding. It hunts them at every turn, separated from the world above in its lair of damp stone corridors and abyssal chambers. Nova soon discovers that the horrors her sister endured was only the surface of something far older and more sinister that indeed the government did cover up. Only they realize this a little too late. Will Nova and her team be able to escape with their lives, or succumb to the evil that was caught on tape all those years ago?