Tune In: The Beatles: All These Years by Mark Lewisohn. I picked it up as a Beatles fan, but it actually reads more like "how did the Beatles happen" - a social history of the times, the factors that led to each of their development as artists, and their iterative development into the group that we know as The Beatles. Put another way, it's a deep dive into the four founders of one of the most successful artistic organizations of all time and their search for product-market fit. This is also part 1 of 3, ending when they finally achieve PMF, releasing their first number one record.