FBI Special Agent Jonah Briggs and Dr. Cassian Holt's Critical Trace Unit faces its deadliest test: an engineered virus unleashed in St. Louis. The source points to Helix Core, a biotech firm quick to frame a disgraced scientist. While Cassian follows the evidence, Jonah's instincts scream foul play, creating a rift that threatens their new partnership.

But as the team uncovers the truth, a terrifying reality emerges: the conspiracy runs deeper than one building. The real target is the shadowy corporate power that has haunted them since their first case, and stopping the city-killing "Vector Burn" is their last chance to expose the mastermind behind it all, or die trying. This is the final battle.