“Problems of Life and Mind in Late Victorian Speculative Fiction” contributes to the thriving study of literature and science in the Victorian period by presenting three case studies in non-realist literature’s mediation of scientific debates at the end of the nineteenth century. In Arthur Machen’s early Weird tale “The Inmost Light” (1984), H. G. Wells’ science fiction novels The Time Machine (1895) and The Island of Doctor Moreau (1896), and Vernon Lee’s ghost story “Oke of Okehurst” (1884), we find answers to interdisciplinary questions about agency and purpose in human action, biological classification, and our ability to perceive and understand other people. In the second half of the nineteenth century, the emerging sciences of neurology, psychology, and evolution made human bodies newly problematic. These bodies were increasingly understood to be made of atoms and meat, shaped by evolutionary biology and their own histories of sensory experience, and subject to laws of physics and physiology. The texts in this dissertation respond to these limits by imagining alternative realities. Rather than being reconcilable with known natural laws, the worlds of these speculative texts go beyond them: they prompt an imagining of other configurations of natural law, possibilities rather than facts, carrying readers beyond what could be supported or countenanced in scientific discourse. In this way, these texts prompt readers to imagine the shape of solutions for problems that feel irresolvable in consensus reality. In calling these texts “speculative fiction”—rather than the more usual term “Gothic fiction”—I hope to draw attention to their cognitive work. Against a critical tendency to read these genres as ‘anxious’ responses to contemporary science, I argue that they offer creative and critical thought about the structure of the world, the body, and the human mind.