In a chat with showrunner Rob Daherty, we learned that viewers are bound to uncover "some bigger pieces of the puzzle" involving Sherlock's stay in London. And to whet your appetite just as more, here's the EP's official statement --
“I don’t think I’m giving too much away to say that Watson was onto something in the pilot. There’s a story to tell as to how Sherlock came to be in the States, how he came to spiral into addiction. We want to give Joan and the audience pieces of this mystery so they have them when we finally get more explicit about how he lost control and ended up in New York. "
'Elementary' airs every Thursday on CBS.
Source: TV Line