The Beatles had just quit the stage, and Sgt. Pepper is the record of a band with nowhere to be but the studio. The conceit is a fake band, an alter-ego the real one hides behind, which freed them to try anything: a circus organ here, an Indian drone there, an orchestra told to climb from its lowest note to its highest without instruction.

Released in 1967, it was built to be heard whole, start to finish, with no gaps and a sleeve full of faces to study while you listened. Inside that frame sits a run of songs that have very little to do with each other except a shared appetite for going further than the last track did. Some of it is whimsy, some of it is grief dressed as whimsy. It became the album people point to when they argue about when pop grew up.