Most tunes live in one key. “Giant Steps” lives in three at once — three tonal centres a major third apart, splitting the octave into equal parts. The music tours all three, and each major chord is announced by its own dominant a step ahead of it, so the key floor keeps dropping out from under you. It's the rite-of-passage progression, and the same major-third trick (“chromatic third relations”) hides inside older standards like “Have You Met Miss Jones.” Pick a starting key and watch the three centres fall out.