This article examines Peter Ackroyd’s popular Gothic novel The Casebook of Victor Frankenstein (2008), which is a reimagining of Mary Shelley’s famous Gothic novel Frankenstein, or, The Modern Prometheus ( 2003). The basic premise of Ackroyd’s narrative seemingly resembles Shelley’s own, as Victor Frankenstein woefully reflects on the events that have brought about his mysterious downfall, and like the original text the voice of the Monster interrupts his creator to recount passages from his own afterlife. However, Ackroyd’s adaption is instead set within the historical context of the original story’s creation in the early nineteenth century. Ackroyd’s Frankenstein studies at Oxford, befriends radical Romantic poet Percy Bysshe Shelley, moves to London to conduct his reanimation experiments and even accompanies the Shelleys, Byron and Polidori on that fateful holiday when the original novel was conceived. This article explores how Ackroyd’s novel, as a form of the contemporary ‘popular’ Gothic, functions as an uncanny doppelgänger of Shelley’s Frankenstein. By blurring the boundaries between history and fiction, the original text and the context of its creation haunt Ackroyd’s adaptation in uncannily doubled and self-reflexive ways that speak to Frankenstein’s legacy for the Gothic in popular culture. The dénouement of Ackroyd’s narrative reveals that the Monster is Frankenstein’s psychological doppelgänger, a projection of insanity, and thus Frankenstein himself is the Monster. This article proposes that this final twist is an uncanny reflection of the narrative’s own ‘Frankenstein-ian’ monstrous metafictional construction, for it argues that Ackroyd’s story is a ‘strange case(book)’ haunted by the ghosts of its Gothic literary predecessors.