Moving on, within the scope of our spoilers umbrella, here are the Sherlock Holmes scoop you can count on in the next episodes! Our source? The EP himself, Rob Daherty! Enjoy them while it's still hot!
“Each of the two episodes has its own case, but there’s some connective tissue in the B-story [involving] Joan and her curiosity about Sherlock’s past. She’s always pressing him for more information in the hopes that it will help her be a better companion to him. But Sherlock is in so many ways a locked vault inside another locked vault. We get into the mythology a little bit more."
Source: TV Line