Mycroft never knew how many times Sherlock had begun letters to Watson during those three years, nor how many timetables had been consulted for the fastest route back to London. He suspected, of course, but that was hardly the same thing as certainty. Then again Sherlock would never know how many times Mycroft had taken the role of cabman again, to find a way to keep a curious eye on the one man his feckless brother had ever called a friend.
A friend indeed, Mycroft realized, while he watched Watson mourn, and wished that he had one of his own.