Sherlock (Benedict Cumberbatch) is not dead: this much we know. But how did he survive his leap off the roof of St. Bart's Hospital? There are many theories, but none of them matter to John Watson, who is less concerned with how his friend survived than with why his friend didn't let him know he was alive. Sherlock returns to London with an assignment (stop an impending terrorist attack on the city) and a plan (restore the old Sherlock-John partnership). When he finds that his brother Mycroft's warning that John has moved on with his life is true, will Sherlock have to accept a new reality and a new partner?