Dr. Carl Stoner, a dedicated herpetologist with an obsession for the secrets of reptiles, discreetly sells a mysterious creature to a carnival owner, keeping the deal cloaked in secrecy. He then enlists college student David Blake as his assistant, claiming that a former colleague is unavailable due to a family emergency. However, David and others remain unaware of Stoner's increasingly delusional state of mind, which leads him to indulge in fantastical thoughts.
Stoner begins administering injections to David, which he claims are meant to protect him from snake bites within their laboratory, but a darker purpose lies beneath the surface. As the treatment continues, David starts to experience an alarming metamorphosis; his skin begins to distill away its humanity, reminiscent of the shedding of snakeskin. His dreams are plagued with terrifying nightmares, and his physical condition deteriorates rapidly, much to Stoner's dismissal, which he attributes to venom effects.
Amidst this chaos, David finds romance with Kristina, Stoner's daughter, even as her father strongly warns her against any intimate involvement. Unbeknownst to them, David's transformation takes a darker turn as his skin acquires a greenish, scaly texture. The injections seem to consume his identity, with Stoner justifying his actions as protective measures.
One night, David awakens to a horrifying reality—his own reflection has become alien. In a fit of terror, he screams, and as he stumbles through the lab, Stoner administers another injection just as Dr. Daniels arrives, suspicion clouding his demeanor. Stoner quickly hides David in a corner, but fueled by primal instincts, David pushes himself to a window, revealing his grotesque form to Daniels. In a desperate act, Stoner knocks Dr. Daniels unconscious and tragically feeds him to a python.
As the chaos escalates, Kristina becomes frantic when she stumbles upon a freak show featuring a "snake-man" strikingly similar to Stoner's former assistant. Horrified and driven by a sense of urgency, she rushes back home, determined to rescue David from the horrifying changes he is undergoing. Meanwhile, Stoner meets his own demise as he succumbs to the venom of a live king cobra found in their lab, while David's transformation reaches its unsettling climax.
Kristina returns only to find her father lifeless, with the very snake coiling ominously beside him. Understanding that something is gravely amiss, she races to alert the police. Their timely arrival sees them shooting the serpent just as they approach the lab, where a mongoose attacks David, attempting to deliver a lethal bite. The officers hesitate, unsure how to act, while Kristina cries out in desperation for David. The film culminates in an abrupt ending, leaving the fates of Kristina and David shrouded in darkness and mystery, inviting viewers to ponder the sinister consequences of obsession and transformation.
