Somewhere inside London's Abbey Road studios, hidden behind an unmarked, triple-locked, police-alarmed door, are some of the most valuable artifacts of twentieth-century music: the raw tapes of every recording session in the nearly eight-year studio career of the Beatles. One of the most remarkable facts about the Beatles is that they released only ten and a half hours of music during their years together--the contents of the group's twenty-two singles and fourteen albums. Yet the tapes inside the Abbey Road archives, it turns out, contain more than four hundred hours' worth of Beatles recordings. The collection extends from June 6, 1962, the date of the audition that narrowly persuaded George Martin, a producer at EMI Records, to sign the Beatles, to January 4, 1970, when Paul McCartney, George Harrison, and Ringo Starr (John Lennon was in Denmark on holiday) recorded the final overdubs for what amounted to the group's farewell album, Let It Be. In between are tapes of everything else, stored in red-and-white cardboard boxes the size of large telephone books. Pick a favorite Beatles song; the archives hold not only the master tape of that song as it is heard on the album but also the working tapes that trace the song's evolution from its first run-through to its polished final version. There are also lots of off-the-cuff jam sessions, arguments, horseplay and studio chat, as well as a few songs the general public has never heard. In the course of the research for this book, I was fortunate enough to gain access to these archives on two occasions. While on assignment for The New Yorker, I spent the equivalent of six full days inside Abbey Road, listening to fifty hours of tapes of the Beatles and of the solo work of John Lennon. I sometimes felt during those days as though I had been allowed to watch Picasso sketch, and never more so than on the afternoon I listened to all seven takes of "A Day In The Life," the closing song on the Sgt. Pepper's Lonely Hearts Club Band album. John Lennon recalled Sgt. Pepper as "a peak" in the Beatles' career, a time when "Paul and I were definitely working together, especially on 'A Day in the Life.' " Indeed, "A Day In The Life" may be the ultimate McCartney-Lennon collaboration, a classic example of how the songwriting style of each man perfectly complemented that of the other. Although John would later confess that he and Paul wrote many songs "eyeball to eyeball," especially in the early days, their usual practice by this time, January 1967, was for one of them to provide the missing middle or accents to a song that the other had already almost completed. In the case of "A Day In The Life," it was Paul who made John's composition whole. Lennon had the melody and story line--the man who "blew his mind out in a car," the English Army that "had just won the war," the "four thousand holes in Blackburn, Lancashire"--but the song needed something more. Lennon didn't like laboring over songs, preferring instead the Zen purity of inspiration, so when he got stuck after completing the main verses he set the song aside. "I needed a middle-eight for it [the "middle eight" is the middle of a song where the tune changes before going back to the original verse], but that would have been forcing it," he later explained. "All the rest had come out smooth, flowing, no trouble, and to write a middle eight would have been to write a middle eight, but Paul already had one there." Paul did indeed have the fragment "Woke up, fell out of bed..." lying around. The two partners agreed thaMark Hertsgaard is the author of 'A Day in the Life: The Music and Artistry of the Beatles.', published 1995 under ISBN 9780385313773 and ISBN 0385313772.