Dr. Jacob Hood and Rachel Young go to Pooler, Georgia where three otherwise healthy eleven-year-old boys have died from heart attacks. Parents are nervous and the town is anxious to find out what's killing the boys. After exploring environmental issues (eg, minor carbon monoxide leak at the school), it becomes clear that some form of poison is the cause of death, but what is the poison and who is giving it to the boys. When Stephen, the son of the hospital administrator, falls ill, Hood has a new direction: the toxin produced by a toad. The toad isn't native to the region but a local woman, Lizzie Summers, breeds them to harvest the toxin as it can be used in small doses as a medical treatment. It turns out none of the boys tested positive for the toxin, so it wasn't the cause of the heart attacks, but while visiting Lizzie, Hood notices that Foxglove grows wild and it contains digitalis, a well know drug that can produce heart attacks in high doses.
Unfortunately, all of the boys test negative for digitalis as well. Hood gets the idea to test the the DNA of the victims' blood and discovers that their from a single source and that the killer has replaced their blood with his own. This launches Hood into a cat and mouse game between Hood and Stephen, an eleven year old genius, heavily influenced by Nietzsche who wanted to destroy the weak of his class.