Marshall Cuso shows up in NYC with a mushroom, that can cure any disease or injury; his old classmate, Frances, meets him by chance, but keeps secret that she works for Reutical, a pharmaceutical company.

Marshall is on the run, trying to flee New York; Frances confides to her boss, Rick, about the mushroom; Rick sends her to Marshall's farm to get more, but the situation gets out of hand.

Marshall seeks advice from his old mentor, Hildy. Copano and Harrington are drawn further into the mystery of the mushrooms obtained at the raid. Frances has gone to Geneva with her boyfriend Nick (and Rick) but can't resist the call of the mushroom.

Marshall buys a plot of land near a chemical waste site with a plan to grow more mushrooms. Meanwhile, Frances rushes home from Europe after a huge development. Copano and Harrington investigate a connection between Marshall and Frances.

Frances and Marshall attempt to grow the last of their mushroom supply, hoping their plan works. Copano and Harrington, surveilling Frances and Marshall, run into danger when confronted by a neighbouring BMX gang.

Marshall arrives in jail and learns that some very important people refuse to let him out, while danger lurks around every corner; Frances makes a fateful decision; Copano and Harrington pick up the pieces.