In the not-so-distant future, eighteen-year-old computer hacker Mirabel “Bel” Solís lives under a fabricated identity after her parents were killed by crime syndicate operatives, while she and her older brother Mateo fear the wrath of a crime boss who remains on the loose. When things go south, Bel and Mateo escape to the wilderness, where Bel picks up an unusual signal. Thinking they’ve stumbled onto a high-tech doomsday bunker that may be the safe haven they need, Bel hacks the security system and lands them both inside an underground smart mansion called the Submundo, which she soon learns is home to a beastly cyborg—and he isn’t happy to have visitors.