Part of what makes poison so fascinating is how a small dose of a single substance can cure, but a larger dose will kill. That's a lot of power in a simple leaf or a mushroom or white powder. For the right — or wrong — person, it’s tempting.
Kathryn Harkup is a chemist with an expertise in poison. She’s made a close study of a famous poisoner that employed everything from arsenic to cyanide to knock off close to 300 (fictional) victims: Agatha Christie, the mystery writer.