Scarlett Marlowe, a driven alchemy scholar, is determined to complete her late father's quest to find the legendary Philosopher’s Stone, believed to grant eternal life and turn lead into gold. Her search leads her to Paris, where clues point to the stone being hidden within the catacombs beneath the city streets. Scarlett enlists the help of her ex-boyfriend, George, a skilled translator and archeologist, along with a documentary filmmaker, Benji, to capture the journey. They hire a guide, Papillon, who, along with his crew Souxie and Zed, claims knowledge of the uncharted regions of the catacombs where the stone might be found.

Once inside the underground labyrinth, the team faces a series of cryptic riddles and dangerous obstacles. As they travel deeper, they encounter eerie, unexplainable phenomena that challenge their sanity. The passages seem to defy the laws of physics, and personal demons from the group's past begin to manifest, leading each member to confront their darkest moments. The further they delve into the catacombs, the more they realize that the journey is as much metaphysical as it is physical, with the boundaries between reality and nightmare increasingly blurred.