For talented people to share and use their gifts to full advantage, somebody first needs to ferret them out. In 1879, a Manchester-based medical student and aspiring writer named Francis Thompson received a copy of Thomas De Quincey’s memoir, Confessions of an English Opium-Eater, from his mother. De Quincey’s flowery descriptions of the pleasures and pains of opium stirred Thompson’s unease at the prospect of a medical career and nudged him toward a different path. Already unwell with what was probably his first bout of tuberculosis, Thompson started taking opium himself both for symptom relief and for literary inspiration.

After failing his final examinations, he abandoned his studies to seek his fortune in London as a poet. But his deepening drug addiction triggered a steady de...