In reference to the Rat, Wedding, Bow episodes themselves, Mark Gatiss revealed that The Empty Hearse is only partly based on Conan Doyle's The Empty House, while the 'wedding' episode The Sign Of Three is based on...[potential spoiler follows for those now aware of the source material] the wedding of Watson. In an exclusive scene from the episode, Watson is shown asking Sherlock to be his best man. The as of yet untitled third episode is set to begin filming in September.
“He shoots himself in the brains. You don’t come back from that.”
“A girlfriend?” Moffat laughed, upon questioning. “He’d poison a girlfriend just to see if it worked.” However, all may not be hopeless for the lone-detective as the panel were asked about his assistant Molly’s role in series 3.
“Molly was not meant to be a big part, initially,” they admitted, before Gatiss went on to elaborate that the pair's relationship had become “touching” and Molly was one of the only people Sherlock trusted.
Vertue was more upfront about the pair's future. “Molly and Sherlock are not going to happen the way Tumblr thinks it will happen,” she announced, bluntly, in reference to the site's penchant for unique fan fiction and art.
“Wait ‘til you see what she does this season,” Moffat added cryptically.