The network announced on Wednesday, July 2 that a special episode would air in 2015, followed by three new episodes.
BBC One announced that "Sherlock" would return for a special episode before resuming with the fourth series. The special episode, which begins shooting in January 2015, will be followed by three new episodes, which shoot later in the year.
"A special, plus a new series of three episodes - it's a record-breaking run!" showrunner Steven Moffat said in the press release. "Of course, it's far too early to say what's coming, but we're reasonably confident that the very next thing to happen to Sherlock and John is the very last thing you'd expect."
BBC made fans of the show excited by posting two tweets an hour apart on Wednesday, July 2. The first was a gif of the taxi screen featured in the last episode along with Moriarty's face. The tagline read, "Did you miss me? #221back. #Sherlock". The third season ended with Moriarty announcing his return from the dead while the number 221 refers to Sherlock's flat number on Baker Street. The second tweet was the network's announcement that it would reveal something at exactly 2.21 P.M.
"It's taken a little while to get the dates sorted as none of the boys are exactly sitting back twiddling their thumbs but there was unanimous goodwill to make this work, so we're thrilled that 221b is going to be inhabited again," executive producer Sue Vertue said in a statement.
"Series Four! At last ! It's always special to return to Sherlock but this time it's even more special as we're doing ...a special! Not only THAT, we'll then be shooting three more episodes which will take Sherlock and John Watson into deeper and darker water than ever before," co-creator Mark Gatiss said in a statement. "The whole Sherlock team are terrifically excited to return for four new adventures. The Game is on - again!"
It is yet clear when the special episode will arrive in the States via PBS.