The subject of this article is the evolution of the plot in historical perspective. The material is the unity of medieval Western European works with similar plots, known as the Constance Saga. The study involved its samples dating back to the second half of the 14th century. The aim of the study was to determine the evolution paths of the generalized plot of the Saga in the noted period relative to its state in previous periods. Along the way, the task of deriving a plot formula covering all the examples of the Saga with detailed specification in the form of selected motives was solved, which in turn are combined into two main plot situations and two motive complexes corresponding to these situations. Also, taking into account the derivation of a general formula of the Saga specific works of the indicated period were subsequently identified. The leading research method was motive analysis, and the methodology was historical poetics and literary comparative studies. These formulas of Sagas help to better understand the structure of plots, their similarities and differences, and they also show in which direction the plot tends to change, for example, what genre elements can actively penetrate the original plot and give the event material a new coloring. Medieval literature is well formalized, like examples of folklore, and the technique of presenting plots in the form of formulas for a more visual comparison of various literary texts, what allows achieving significant results in comparative historical research. This is the novelty of the presented study, since until now the selected works were compared to search for individual motivic correspondences, but there were no attempts to derive a general formula for the entire set of works of this group.