In RLSK we read: "Remember that what you are told is really threefold: shaped by the teller, reshaped by the listener, concealed from both by the dead man of the tale.," and this observation is also true for life, not only fiction. This "threefold" perspective takes place in a completely different construction as the one that's discussed below (related to "twofold stories"), with examples offered by Alexander Dolinin and Ricardo Piglia. But then, the theme is now about writing a good short-story, not a novel.  

In his text "The Signs and Symbols in Nabokov's "Signs and Symbols",  Alexander Dolinin (Zembla) writes: "In his famous letter to Katharine A. White, the chief editor of The New Yorker, while explaining the intricate riddle-like structure of "The Vane Sisters," which had been rejected by the magazine, Nabokov mentioned that some of his stories written in the past had been composed according to the same system "wherein a second (main) story is woven into, or placed behind, the superficial semitransparent one." As an example, he named another story with such an "inside"--"Signs and Symbols," which had been published in The New Yorker..."

 

Although he didn't mention Vladimir Nabokov's name and short-stories, Argentinian writer Ricardo Piglia, in "Formas Breves" (1999), offers a set of examples of such "double plot lines," he selected from various other authors. He compares Tchekov's personal annotations concerning the story of a Monte Carlo gambler, who wins a million in the casino and then  goes home to commit suicide,  with Hemigway's "Big Two-Hearted River." stressing the twist in the narrative and a surprise finale  He also cites E.A. Poe, Katherine Mansfield, the Joyce of "The Dubliners", Kafka and Borges to illustrate and describe how these writers dealt with these two distinct narrative strands.* 

It's a pity that Piglia didn't include one more example of authorial tactics, to present his views on Nabokov's "spiritualistic," otherwordly and authorial interventions in the short-story. Piglia believes that any good short-story must carry two narrative lines, a superficial one that's presented in full, and a veiled one which may escape the reader's notice, or results from a stylistic variation of the first one.. He believes that it's the narrator's task to unveil to the reader the hidden story using artificial means that help to unfold its "secret truth, like the one that's hiding beneath the opaque surface of life"**

 

 

 

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*  " A short-story always tells two stories. The art of the short-story teller derives from his ability to hide a second story in the interestices of a completed text. A visible story veils a secret story being narrated in an elliptic, fragmentary way. A surprise effect usually arises when the secret story surfaces. "
"Two stories in one require two different causal systems or two antagonical narrative logic - their cross-over point lies at the heart of the story's construction. 
What is superfluous in one story, is fundamental in the other and this is not a question of any hidden meaning that needs interpretation. The enigma resides simply in the enigmatic way a common story is told." 
"After Tchekov, Mansfield and Sherwood Anderson, the tactics of the surprise ending were abandoned to give place to a never-solved tension between the two stories, as found in Hemingway's "iceberg theory."  Kafka tells his secret story with simplicity and clarity, but narrates the visible story in tones of secret mystery  until that one becomes enigmatic and obscure ,instead of the other. For Borges, the two stories are always the same, although they pose different narratological problems -  which he transformed into elements of the plot."  ( note: as usual, my efforts as a translator are not very good. From the information I have about "Formas breves" this collection hasn't been translated into English yet.)

** - "O conto se constrói para fazer aparecer artificialmente algo que estava oculto. Reproduz a busca sempre renovada de uma experiência única que nos permita ver, sob a superfície opaca da vida, uma verdade secreta. 'A visão instantânea que nos faz descobrir o desconhecido, não numa longínqua terra incógnita, mas no próprio coração do imediato', dizia Rimbaud. Essa iluminação profana se transformou na forma do conto."