Hannah McKay was a fifteen-year-old from Clopton, Alabama when her boyfriend Wayne Randall commenced a three state killing spree. She spent six years in Juvenile detention after pleading guilty to being an accomplice. She claimed not to have actually committed any crimes and received immunity from prosecution after agreeing to testify against Randall.
She married an older man but poisoned him when he was pressuring her to have an abortion, in spite of later claiming she wanted to have the child. She inherited her gardening business from her mentor, whom she is later suspected of poisoning with aconitum.

Hannah falls foul of Dexter by poisoning Debra. Hannah had tried to form a truce with Deb but she declined. She spiked Debra's drinking water causing her to pass out while driving. Dexter later gives Deb evidence to prove Hannah poisoned Price. Debra has Hannah arrested.