Casey, a curious and bookish 12-year-old, leads a ragtag afterschool "Artifact Club" with three friends: techie Leo, skeptic Tanya, and conspiracy-loving Benji. They're known for investigating weird urban legends at their middle school, most of which turn out to be janitor closets and rusted tools.
Benji hears about a mysterious briefcase locked away in the old storage wing of the school basement—allegedly sealed off after a "screaming incident" in the 1980s. Casey, skeptical but intrigued, convinces the group it's their duty to investigate before it's lost to summer cleaning crews.
Sneaking in after hours, the club finds the storage room and uncovers the briefcase under a pile of ancient textbooks and sports trophies. It looks ordinary—except for the strange locking mechanism covered in faded warning symbols.
When Casey cracks the lock using a combination hidden in an old yearbook photo, the case springs open. A coiled green snake inside rears up and lets out a humanlike scream—causing lights to flicker and shelves to topple. The snake doesn't attack but seems "programmed" to react.
Leo examines the case and discovers circuitry and speaker systems embedded in the snake's body—revealing it to be an advanced animatronic, possibly military-grade. There's a serial number tied to a long-defunct Cold War-era science program run by a government contractor that used their school building long ago.
Clues in the briefcase lead them to a sealed wing of the school's original blueprint, where they discover an abandoned surveillance lab hidden behind a false wall. Old photos and notes hint the case was a psychological weapon—designed to disorient enemies with "impossible sound."
As the kids debate whether to tell anyone, men in nondescript suits show up at the school claiming to be from a "Department of Environmental Safety." They're really after the case. The Artifact Club barely escapes with the help of Benji's homemade distractions and Casey's quick thinking.
They decide to re-hide the case somewhere safer, deep in the school's ventilation maze, leaving behind fake decoy files. Casey writes up the mission as their first true discovery—and the club is more united than ever. The final scene shows one of the agents holding a yearbook with Casey's face circled.