La trama celeste is a book by Bioy Casares. It is a collection of short stories and it includes a work with that same name.
La trama celeste short story
A soldier must pilot a new plane. He suffers an accident and is injured. He is interrogated and the army does not believe his is from Argentine. They mistake him for a spy. He calls his friends and nobody recognizes him. He cannot explain the situation, but a friend of him, the author, helps him. The author discovers the truth: he has travelled to a parallel universe, a little different from this.