Ian Leslie’s “John & Paul: A Love Story in Songs,” takes a detailed look — 426 pages — at how John Lennon and Paul McCartney worked together from their meeting as teenagers until John’s death. Book Review: ‘John & Paul’ explores complex ties between Lennon and McCartney Had McCartney not decided at age 15 to go hear Lennon’s band playing in a Liverpool suburb, the world would have been denied the multitude of Beatle songs that brightened a generation and brought escalating musical innovation to rock music. As Leslie affirms in the book, Lennon and McCartney early on developed a personal and creative chemistry that allowed them to elevate each other’s work to the timeless song classics still heard around the world. And into that relationship dives Leslie, analyzing the mountain of articles and books written about the Beatles and interpreting messages the two men were sending to each other in their solo songs, particularly after the band’s break-up when both were writing and performing as solo acts. Leslie focuses on exploring the often-tortured relationship …