This popular piano sonata has the recapitulation of the first movement in the wrong key. Tsk, tsk, tsk. Whose and which? (This one should go fast)

Mozart K.545

Correct! Good for you Monica. Many know this work or would instantly recognize it, but perhaps didn't realize this theoretical feature. The 1st movement is in C Major. The Exposition does the coventional modulation to the dominant key (up a 5th). However, at the end of the short development section, instead of preparing for a return of the tonic key for the recap, Mozart instead prepares for the opening music to return in the subdominant ket of F major. Why would he do this? I can only think of one reason: the same path/pattern used in the Exposition (i.e. the modulation up a 5th) here will now return the music to the tonic for the ending.

Yipee....what do I win?