“MY NOVELS CONTAIN a typically postmodern feature — namely, double coding,” said medieval scholar and semiotician Umberto Eco in “Confessions of a Young Novelist,” his 2008 Richard Ellmann Lecture Series in Modern Literature at Emory University. By double coding, he meant the pairing of “intertextual irony: direct quotations from other famous texts, or more or less transparent references to them,” and “implicit metanarrative appeal,” or “reflections that the text makes on its own nature, when the author speaks directly to the reader.” This might enable Eco to separate gold from dross, to establish “a sort of silent complicity with the sophisticated reader” at the expense of those who “los[e] an additional wink.”

Eco’s sixth novel, The Prague Cemetery, assays just such a duplicitous act. Its main character, Simone Simonini, is a professional counterfeiter and spy whose humble beginnings as a forger in a Piedmont notary’s office pave the way for his recidivist tendencies. A wily parvenu, Simonini infiltrates the Paris Commune, jails and murders his collaborators, masterminds the Protocols of the Elders of Zion (a false account of rabbinical speeches proposing Jewish world domination, apparently given at a gathering in the Prague Cemetery of Eco’s title), and pens the memo that inspired the Dreyfus Affair. On occasion he masquerades as Abbé Dalla Piccola, a priest, in order to gather information on religious orders. The narrative is structured as an epistolary dialogue between Simonini and Dalla Piccola in their shared diary, which, like Nikolai Gogol’s “Diary of a Madman,” chronicles Simonini’s descent into madness. The hope is that through telling the tale, “the traumatizing element reemerges,” Simonini says.

To many readers, The Prague Cemetery will seem an antic tour through the byzantine depths of nineteenth-century Europe, a tour frustrated by Simonini’s dual personalities, vitriolic anti-Semitism, and mordant misanthropy (Masons and Jesuits are equally subject to his distaste, as “people are never so enthusiastically evil as when they act out of religious conviction”; women are “just a substitute for the solitary vice, except that you need more imagination”). But what is Eco’s “intertextual irony”? What is being encoded, and what kind of reader perceives it?

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In fact, it’s a third presence, the gendered but unnamed Narrator, who holds the key to Eco’s artful hoodwinking of his readers. To understand his function — his mastery over this labyrinthine narrative, and his appeal to the “sophisticated” reader — it’s worth looking back at Eco’s commentary on two of his previous novels, which carefully match prose with period:

Once an author has designed a specific narrative world, the words will follow, and they will be those that the particular world requires. For this reason, the style I used in The Name of the Rose was that of a medieval chronicler: precise, naïve, flat when necessary (a humble fourteenth-century monk does not write like Joyce, or remember things like Proust) [...] In The Island of the Day Before, the cultural period was the determining factor. It influenced not just the style but the...