As a amateur Composer myself I find modern compositional techniques to be a mess. Writing music that no one listens to, contrary to the current contemporary approach of "dumbing down" and endless copy and paste hooks and refrains.
This book explains quite thoroughly: modern harmony of a variety of composers eg. Schoenberg, Prokofiev, Hindemith,etc. The technicalities are coherent and engaging enough for a post theory grade 8 student and I highly recommend it to musicians who are well versed in Schenkerian analysis and Gradus Ad Parnassum (study of counterpoint).
I started reading this book primarily because of my curiosity in prokofiev's compositional approach, and whether it was possible to have a tangible explanation for his "sound". Because general music theory (abrsm) doesn't go into depth on 20th century music save for 12 tone serialism and the French school eg, Debussy & Ravel.
If you are wondering: "why does this sound weird but so appealing at the same time?" Then I'd say "start with this book". I think that it is a Musician's job to explore all spectrums of harmony for musicianship' sake, And by that acquiring a firmer command at the instrument and music.