As our earliest ancestors migrated out of Africa, they encountered entirely new floras. By sampling these, they found plants that appeared to (and sometimes did) heal wounds, cure maladies, and ease troubled minds. This process of discovery continues today, as multinational pharmaceutical companies bioprospect in the globe's remaining wild places for the next tamoxifen or digitalis.

The gardener and botanist David Stuart tells the fascinating story of botanical medicine, revealing more than soothing balms and heroic cures. Most of the truly powerful and effective medicinal plants are double-edged, with a dark side to balance the light. They can heal or kill, calm or enslave, lift depression or summon our gods and monsters. Often the difference between these polar effects is a simple change in dosage.

Stuart chronicles the tale of how the herbal materia medica of healing and killing plants has sparked wars, helped establish intercontinental trade routes, and seeded fortunes. As plant species traveled the globe, their medicinal uses evolved over miles and through centuries. Plants once believed to be cure-alls are now considered too dangerous for use. Others, once so valuable that they sowed the wealth of empires, are merely spices on the kitchen shelf.

David Stuart recounts engrossing human stories too, not only of the scientists, explorers, and doctors who gathered, named, and prescribed these plants but also the shamans, magicians, and quacks who claimed to possess the ultimate herbal aphrodisiac or elixir.