It’s highly possible that Sherlock really would sit there as his apartment steadily fills with water, but would John?
All will become clear, of course, and the tagline to the teaser, “It’s Not A Game Anymore”, falls in line with Gatiss’ previous comments that this season is explicitly darker.
Season 4 is highly anticipated; the (really) short seasons mean that they always seems to be over just as they’re beginning, which in turn leaves fans wanting more.
And, given that Sherlock’s apartment is upstairs, poor Mrs. Hudson must be swimming for her life down below.