In the first meeting of my first-semester theory class, I often examine the opening eight measures of the Adagio variation of Mozart’s so-called “Twinkle Variations,” K. 265. Presenting the excerpt as a detective story, in which the class seeks to discern the theme that structures the ornate variation (even in its absence), has proven a compelling way to discuss a handful of important topics that are treated more completely later in the theory curriculum. The foreshadowed topics include theme and variations form; triadic arpeggiation; melodic shape and gesture; cadence; ornament; melodic fluency; gap/fill; musical topic; and genre. The lesson has two further benefits: first, it is a productive way of breaking the ice on the first day of class: the ludic approach (and the beauty of the variation) make it easy to get a discussion going about a piece of eighteenth-century instrumental music. And second, it tacitly functions as a diagnostic, in that it allows me to measure the abilities and backgrounds of entering students quickly in a low-pressure situation. In this lesson plan, I sketch the order and manner in which I present the material to my first-day theory class.