Robert Louis Stevenson’s “The Strange Case of Dr. Jekyll and Mr. Hyde” is an oblique and artful Gothic tale framed as a detective story. The truth seeker is Jekyll’s lawyer, Utterson, the book’s most prominent character. Jekyll — the gentleman who dabbles in chemical self-transformation — appears only intermittently, never fully speaking for himself until the end, when he discloses the details of the disastrous experiments that unleashed his primitive alter ego. The novel isn’t a conventional horror story, lingering on the macabre for its own sake, but an allegory of the divided self, perhaps also a meditation on addiction. Stevenson dramatizes human duality but doesn’t analyze its causes, treating it as pervasive and fundamental. For him, the Jekyll-Hyde split is the split in all of us, between the animals we evolved from and the angels we aspire to be.