Highly Suspect is written in a modified 32 bar/ballad form (AABA) and is in the key of Bb minor. The final A section ends differently than the 1st A. The piece demonstrates the use of altered chords, including the Neapolitan 6th (bII), iv, bIII, bVI, iio, viio7, and the Picardy Third. There are also four significant modulation points: common chord, altered chord, monophonic, and sequential, respectively. 

A section introduces main theme. Tenor and bass rotate between ascending sequences and Alberti bass. M. 3 uses a secondary dominant to the III. M . 4 begins common tone modulation between a ii0 and Gb (Gb common tone). M. 5-7 utilize common harmonic progression sequence for a major key. M. 7 uses an unusual minor secondary dominant to bring us back to the starting key of Bb minor. The second ending of the A section throws the harmony into disarray for a brief moment as the bII hands the melody to a V, before chromatically ending up on a descending C7 arpeggiation as part of the monophonic modulation.

The B section begins in the key of F, but quickly moves on to a bIII. The bIII and I go back and forth for 2 measures to create tension, before ‘resolving’ to a Bb minor chord, the iv, in m. 13. M. 14 repeats the sequence but rotates between iv and the minor i. M. 15 mirrors the sequence an octave lower but changes the chords to a IV and I, which offers a really interesting harmonic sequence. M. 16 starts on a bVI before resolving to the I using a iio, V, I sequence. M. 17 mirror the same sequence but uses a viio, V, I, resolving back to the major I (Picardy Third). M. 18 b.3 uses a quintuplet sequence to help better prepare the listener for 2 measures of triplets in the melody as part of the sequential modulation. This modulation consists of 2 measures identical besides the key. The bII is used in both to prepare the V chord. M. 21 pauses briefly and uses the repetitive motif in the Alto to tonicize the V in the upcoming transition to the A section.

The third A section follows a separate ending to the first two and does not include a common tone modulation. Instead, the melody modulates directly to Db, the relative major, which the piece ends in.