Synopsis:

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When bodies start appearing around St. Bernard Parish with mysterious toxins in their systems, Homicide Sergeant Lance Knight finds himself investigating a series of seemingly unrelated high-profile murders. The only common threads are strange voodoo poppets left at crime scenes and Queen of Diamond playing cards with an increasing number of punch holes found with each victim.

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The investigation takes an unexpected turn when Lance's girlfriend Lexi Goodman is revealed to be an undercover FBI agent investigating Sasha Volari, a local drug lord known for using snake venom in her products. With help from Gina Goodwin, the coroner and herpetologist, Lance discovers the murders are connected by a rare and deadly snake venom from the Golden Lancehead, a species not native to Louisiana.

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As Lance gets closer to the truth, he becomes a target himself. After surviving multiple snake-related attacks, including a rattlesnake in his bed and a snake planted in his car causing him to crash, Lance begins to suspect there's more to the case than Sasha Volari's drug operation.

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Following Lexi to an abandoned building, Lance discovers she is actually the killer, targeting men she believes take advantage of women. In a climactic confrontation, Lance manages to turn Lexi's own murder weapon – a syringe filled with snake venom – against her, though he's bitten by a snake in the process. Fortunately, the snake proves to be non-venomous, and Lexi succumbs to her own poison.

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In the aftermath, Lance, Gina, and Captain Donovan are appointed by the Governor and FBI Director to lead a new specialized task force: The Poison ID Unit, dedicated to investigating crimes involving poisons and toxins. This sets up the foundation for an ongoing series of investigations into unique and deadly poisonings.