Sherlock Season 4: 9 Big Questions After 'The Lying Detective' 

9. Is Irene Adler Coming Back?

For years, fans have been left wondering what exactly happened to Irene Adler. She hasn't been seen - outside of Sherlock's mind palace, anyway - since he apparently saved her way back in A Scandal in Belgravia.

It's revealed this week, though, that the pair are still in occasional contact (of a suitably flirtatious manner, of course), and Watson urges him to make something more of it.

Does that mean we're in for a return of Lara Pulver's dominatrix? There's no denying it'd be welcome, given she was a great part of the show and has excellent chemistry with Cumberbatch, and it'd be the tying up of another (somewhat) loose end. If this is indeed the last series of Sherlock, a reunion with Adler would seem fitting.