A stylistic shibboleth of musical romanticism and early modernism, the breakthrough figures as a salient expressive device in many of Webern’s tonal compositions. This chapter sheds light on the aesthetic function that energetic thresholds fulfil in Webern’s early work, through a close analysis of the Piano Quintet (1907). Described by Theodor W. Adorno as an ‘amalgamation of Brahmsian with Wagnerian elements’, the quintet engages a complex dialectic between ‘formal’ and ‘material’ meaning strata. Linking this dialectic to what is termed the ‘agitating impulse’, a motivic idea set up in the opening bars that adamantly strives towards its resolution yet which is consistently frustrated, this chapter construes the various waves pervading the work not as emancipatory gestures but corporeal manifestations of a subcutaneous anxiety. As such, it is suggested that the quintet offers an original contribution to ‘Romantic’ sonata form practices, and a novel interpretation of the breakthrough.