Think back over the chapters. In a back room in Chinatown, two old men bend over a book older than the city outside, hunting the proper supper for a cricket — and find a princess who answered the question centuries ago. Days later, under Times Square, a mouse dances on a ledge, a cat hums with the radio, and a cricket discovers that every song in the world will stay with him after a single hearing. Then a box of matches tips, flame runs along the newspapers like a living thing, and the happiest night of Chester’s new life ends with him blinking in the smoke of the home that took him in.

When the first radio stations began broadcasting in the 1920s, something changed forever: music learned to travel. A singer in one room could be heard, at the same instant, in a million rooms. The trick works in three steps. At the station, a microphone turns sound into an electrical pattern, and a tall tower broadcasts that pattern outward in every direction as radio waves — ripples of energy that are completely invisible and utterly silent as they pass through air, walls, and even people.

In each home, a receiver catches the waves, turns the pattern back into sound, and pours the song from its speaker. By 1960, radios sang everywhere — kitchens, taxicabs, corner newsstands — and a listener could hear more music in a week than a villager of old heard in a lifetime. Stations played through the night, mixing opera, jazz, and popular songs, and none of it cost the listener a penny. For most people the radio was company. But for anyone learning music, it was a school with the world’s greatest teachers, holding class all day long — free to every listener with an ear good enough to keep what it heard.

No right or wrong — close the screen and tell someone nearby what happened in this part. Can’t find anyone? Tell yourself out loud. The moment you teach it, you truly understand it.