When Watson joins forces with Holmes and Kitty to locate a missing nurse she used to work with, the woman’s trail leads them to another person who has recently disappeared.
Cello Suite No. 1 in G Major, BWV 1007: I. Prelude — Erling Blöndal Bengtsson
Watson enters the brownstone and finds Sherlock lying on the floor, listening to music, he tells her that he's pondering eternity they then talk about their current case and their theory's on it.