Narrative Passing in Mary Shelley's Frankenstein

The narrative structure of Mary Shelley's Frankenstein occurs in passes, like a relay race with three runners, who each pass the baton in a circuitous pattern. Altogether, there are four passes. Starting with voyager Walton, who opens the novel with a series of letters to his sister Mrs. Saville; then to the Frankenstein's narrative, the ardent student, creator, sufferer; he passes the baton to the monster. The narrative at this point runs counter, where the monster relays back to Frankenstein's voice, then lastly to Walton and his letters to his sister. Keep in mind, though, that the whole of the story is conceived (after all, this is a novel about conception) via the letters from Walton to his sister, from December 11 to September 12:

I have resolved every night, when I am not engaged, to record, as nearly as possible in his own words, what he has related during the day. If I should be engaged, I will at least make notes. This manuscript will doubtless afford you the greatest pleasure: but to me, who know him, and who hear it from his own lips, with what interest and sympathy shall I read it in some future day!