This paper focuses upon how one hears the bizarre slow introduction of Mozart's String Quartet K. 465, first movement entitled “Dissonance.” For this task, I have incorporated and criticized Heinrich Schenker's analytic graph and perspective of the slow introduction and finally proposed a new analysis that takes the prominent role of and its harmonic supporter V7 as a main theme. My graph is different from Schenker's not only in that I have chosen at m. 7 as earlier as Schenker, but also in that I saw the slow introduction as an essential part, not simply as a prefix to the following body. The abrupt register transfer (mm. 31-35), voice cross between the two violins (m. 35), motivic parallelism found at mm. 8-13 etc. open a possibility of the alternative reading. The alternative graph represents the structural as well as aesthetic characteristics of the slow introduction, not only because the dissonant and unsettled quality originated from the tonal conflict and ambiguity is reflected on the deep-level structure, but also because what I call “the structural dissonance” that governs the entire introduction has influenced upon the exposition and thus integrated the two formal sections into a inseparable structural unit.