The story begins in Grand Central Terminal, where Percy, Annabeth, Jason, and Piper are on a seemingly ordinary day—but with a mission, of course. Annabeth leads the group with an ancient map labeled "Substations Forgotten: A Guide to New York’s Hidden Depths," which supposedly reveals the location of a cursed subway station tied to Nyx, the goddess of night. Percy’s sarcastic narration highlights the group’s banter as Jason complains about glowing puddles and Piper teases him about his unease. Annabeth declares that a faded staircase marked “restricted” is their entry point. She explains that the station, abandoned after mysterious disappearances, might house the Eye of Nyx, a powerful artifact tied to eternal darkness. Percy quips about their luck in always finding the world’s most dangerous problems, while Jason and Piper exchange wary glances. Descending the stairs, the air grows cold, the lights flicker, and the shadows seem to move, setting the stage for the adventure ahead.

The group descends into an abandoned subway station, following a cryptic map to find the Eye of Nyx. The eerie setting grows darker as they encounter a glowing mosaic with carvings of constellations from an unknown sky. Annabeth deciphers an inscription: "Only those who walk in shadow shall pass unscathed." Shadows begin to take humanoid forms, watching the group as they realize the mosaic requires a test of courage. Jason steps onto the mosaic, letting shadows engulf him. He emerges unharmed, triggering a hidden door. The group advances, unaware that Jason has been marked by something sinister.

The group enters a twisting underground maze, walls pulsing with faint, otherworldly energy. Annabeth navigates, but the paths shift unpredictably. Shadows flicker along the edges, whispering cryptic warnings. They stumble upon a broken pedestal holding a shattered artifact—likely part of the Eye of Nyx. Before they can investigate, a massive, shadowy Minotaur emerges, its roar shaking the labyrinth. A chaotic fight ensues, with Percy distracting it while Annabeth realizes the walls react to sound. Jason and Piper create a distraction using their abilities, collapsing part of the maze on the Minotaur. They grab the artifact shard and flee deeper into the maze.

The group reaches a hidden chamber where the shard begins glowing intensely, resonating with Jason's "mark." The room pulses with strange energy, and Jason becomes increasingly agitated, hearing whispers urging him to complete the Eye. The others notice his behavior and grow wary, suspecting the shard is influencing him. Annabeth tries to analyze the shard’s power, but Jason snaps, his powers surging uncontrollably. A heated argument breaks out as Jason struggles to explain the whispers in his head. Percy demands they destroy the shard, but Jason insists they need it to understand the Eye's purpose. The tension escalates until Piper calms everyone, reminding them they need to trust each other. They leave the chamber with the shard, but the unease remains.

The group emerges into an ancient amphitheater where the shard activates a hidden mechanism, piecing itself into a larger structure. The Eye of Nyx begins forming, emitting waves of dark energy that threaten to consume the group. Jason, still under its influence, steps forward, drawn to its power. Percy, Annabeth, and Piper frantically try to stop him, using their skills to destabilize the growing artifact. Piper uses her charmspeak to reach Jason, breaking the shard’s hold over him. Realizing the danger, Jason channels his powers to destroy the Eye, causing a massive explosion. The amphitheater collapses, but they narrowly escape. In the aftermath, the group reflects on the test of their bond and Jason’s struggle to reclaim control over himself.