The Mysterious Freebooter, or Subterranean Horrors did not pause to consider whether the characters and adventures were true to life.  They desired, indeed, not to criticise but to create, and in the winter of 1809-1810 united to produce a terrific romance, with the title Nightmare, in which a gigantic and hideous witch played a prominent part.  After reading Schubert’s Der Ewige Jude, they began a narrative poem dealing with the legend of the Wandering Jew,[91] who lingered in Shelley’s imagination in after years, and whom he introduced into Queen Mab, Prometheus Unbound, and Hellas.  The grim and ghastly legends included in “Monk” Lewis’s Tales of Terror (1799) and Tales of Wonder (1801) fascinated Shelley;[92] and the suggestive titles Revenge;[93] Ghasta, or the Avenging Demon;[94] St. Edmund’s Eve;[95] The Triumph of Conscience from the Poems by Victor and Cazire (1810), and The Spectral Horseman from The Posthumous Poems of Margaret Nicholson (1810), all prove his preoccupation with the supernatural.  That Shelley’s enthusiasm for the gruesome and uncanny was not merely morbid and hysterical, the mad, schoolboyish letter, written while he was in the throes of composing St. Irvyne, is sufficient indication.  In a mood of grotesque fantasy and wild exhilaration, Shelley invites his friend Graham to Field Place.  The postscript is in his handwriting, but is signed by his sister Elizabeth: 

“The avenue is composed of vegetable substances moulded in the form of trees called by the multitude Elm trees.  Stalk along the road towards them and mind and keep yourself concealed as my mother brings a blood-stained stiletto which she purposes to make you bathe in the lifeblood of your enemy.  Never mind the Death-demons and skeletons dripping with the putrefaction of the grave, that occasionally may blast your straining eyeballs.  Persevere even though Hell and destruction should yawn beneath your feet.

“Think of all this at the frightful hour of midnight, when the Hell-demon leans over your sleeping form, and inspires those thoughts which eventually will lead you to the gates of destruction...  The fiend of the Sussex solitudes shrieked in the wilderness at midnight—­he thirsts for thy detestable gore, impious Fergus.  But the day of retribution will arrive.  H + D=Hell Devil."[96]

That Shelley could jest thus lightly in the mock-terrific vein shows that his mind was fundamentally sane and well-balanced, and that he only regarded “fiendmongering” as a pleasantly thrilling diversion.  His Zastrozzi (1810) and St. Irvyne (1811) were probably written with the same zest and spirit as his harrowing letter to “impious Fergus.”  They are the outcome of a boyish ambition to practise the art of freezing the blood, and their composition was a source of pride and delight to their author.  A letter to Peacock (Nov. 9, 1818) from Italy re-echoes the note of child-like enjoyment in weaving romances: