Based off this doodle my friend made (it's Dean breaking into Sherlock's apartment)

Sam and Dean are on their vacation in London, walking the streets as American tourists with Cas tagging along just because. They walk along Baker Street, just outside John and Sherlock's shared flat. Inside Sherlock is madly bored, and decided to start shooting the wall.

After debate between Dean - who wants to go in and see what's going on - and Sam - who just wants to mind his own business in this foreign city - it is decided that Dean is going to run in and investigate.