This article offers a Schenkerian interpretation of movement 12 from Sergei Rachmaninoff’s All-Night Vigil, also known as Vespers, op. 37 (1915), from the standpoint of tonal duality, known in Russian as peremennost’, or mutability. First, I explore theoretical connections between several concepts related to tonal disunity in Russian- and English-language sources, including tonal pairing, directional tonality, and mutability, and offer my own definition of mutability, understood in Schenkerian terms. I then briefly discuss these phenomena in the style to which the Vigil belongs—the New Russian Choral School. With this theoretical and historical background, I then give a detailed analysis of movement 12, showing that (1) Rachmaninoff inherits mutability from the standard musical practice of the Russian church and (2) mutable relationships penetrate the work from the foreground to the deepest level of tonal hierarchy, at which two Ursätze in different keys are joined together at the same hierarchical level. In the process, I offer a slight adaptation of the Schenkerian background paradigms to accommodate the imperfect authentic cadence with in the soprano, which in Russian church music bears a closural function.