Joan's first trip to London, the trip where she met Mycroft and Lestrade and helped solve a murder, had been more touristy. There had been a fair amount of downtime as Sherlock dealt with being back in London after fleeing in grief and narcotics. This time was supposed to be in and out.

Interesting how quickly and thoroughly things can change.

She squeezes him back, and settles against him to watch.