To get out of helping Kate (Rachael Leigh Cook) on a case involving a millionaire who made his fortunes stealing from nursing home residents, and dealing Donnie’s (Scott Wolf) suggestion that she has romantic feelings for her former professor, Daniel Pierce (Eric McCormack) agrees help to help an environmental activist (Lisa Sheridan) with a bizarre case of several young women in a small town all developing ticks and mannerisms similar to Turrets Syndrome in the space of only a few days (even if that means braving planes, hotel rooms, and angry mobs of locals who will go to any lengths to make sure the plant isn’t closed). The activist believes their conditions may have been caused by harmful chemicals from a nearby plant, but the more he investigates the more Daniel begins to think something entirely different is at play.
Already uncomfortable out of his element, Daniel becomes even more so after he’s findings don’t support those of the activist and he begins to suspect the woman of going to great lengths (even having her assistant shoot at her in public) in order to set the stage for a completely fictitious story designed for a big jury payoff. However, after debunking her story, Daniel and Kate are still faced with discovering what is responsible for the girls’ symptoms and why Daniel finds himself haunted by the victim (Laura Wiggins) of a staged suicide which he believes may also be the cause of a spreading psychosomatic trauma.
To get to the truth of what he believes may be nothing more than mass hysteria caused by a single traumatic event and guilt, Pierce and Kate talk with the first group of girls stricken with the affliction (Vanessa Marano, Damaris Diaz, Lindsay Bushman, Tiffany Boone) but although they discover the event which triggered the disorder none of the four girls are their killer. Eventually Daniel’s hallucination of the girl’s ghost leads Daniel to her illegitimate father (Ray Wise) and their killer (Martha Hackett).
Once again the show uses a psychological trigger or condition to build its mystery of the week around. Sadly, the familial final twist isn’t as compelling (or original) as the guilt of the four young girls and the actions which cause their conditions and more than gave them motive for murder. “Toxic” also gives us Daniel awkwardly confronting Kate about the signals she has been sending out, which doesn’t go well, and the drunken camaraderie in the hotel bar between Kate and Lewicki (Arjay Smith) as the founding members of the Daniel Pierce support group.