The enduring terror of The Great God Pan has been attributed to various factors: degeneration, deep time, the abhuman subject, neurological theories, and sexual mysteries. Connecting and expanding on these analyses, I investigate the terror derived from philosophical and juridical conceptions of consent implicit in contemporaneous debates and legislative changes about vivisection, age of consent, and regulation of venereal disease. While late Victorian periodical and juridical discourse assumes there is safety and justice in the individual’s right and capacity to make decisions about what happens to one’s body, The Great God Pan, I argue, dramatically disquiets these urgent expectations. By compounding an explicitly justified medical invasion with an implied sexual assault, Machen’s tale dramatizes the unsettling indeterminacy of consent at a time when its legal definition has supposedly been fixed. Ultimately, I demonstrate how consent’s hollowness is amplified to terrifying effect in the “suicidal mania” of the main narrative.