It is not rare that the narrative process of fantastic literature presents the characteristics of the detective novel, since it describes inexplicable history concerning the phenomena. Both kinds of literature demonstrate a very similar structures: the event begins with a mysterious affair in a pacific real world and it is developed with an investigation on the happening and it culminates with or without a final explanation. They also have common cognitive bases in the appearance as a genre of literature, since they had been born in the time that it began to bloom the positivism and the determinism, which characterize the two mentioned kind of literature. Whereas the fantastic literature appears as a compensation for excessive rationalism, the detective novel is an absolute belief in the rational power. Due to this different reaction to the rationalism, there is a basic difference in motive of the supernatural and mysterious happening between them. As Todorov indicates, the fantastic text depend on the irrational explanation, whereas the detective novels, on the rational explanation. Our concern is not a mere comparison between both kinds, but the effects of their narrative combination: the application of the narrative technique used in the detective novel to the fantastic literature. The rational and analytic process used to solve the mystery in the detective novel, constitutes its main scheme, but in fantastic literature it works as the auxiliary scheme. In our opinion, if the author uses the method of the detective investigation, its main object does not consist of the solution of the supernatural fact, but of having following three effects: 1) to produce the reality 2) to offer a version between several ones 3) to provoke the active participation of the reader. Also we will observe the contribution of the view of the world presented in the detective novel to the fantastic literature, with which we can have the total vision that it tries to reach the fantastic literature. For this analysis, we have selected 'El otro laberinto' of Adolfo Bioy Casares. The argentine author, considered one of the greatest masters in the contemporary fantastic literature, always took much interest in the detective novels and wrote several ones adapted the parody in collaboration with Borges and Silvina Ocampo. And we hope that this investigation will be a help for the understanding the narrative mechanism used in the fantastic-detective novels.