Sherlock creator Steven Moffat has said the future of the BBC show is uncertain as he does not want to it going "past its natural term".
The fourth series of the detective drama, which stars Benedict Cumberbatch, is currently airing on BBC1.
Moffat said he and Mark Gatiss - who created and write the hugely popular programme - do not want to see the sleuth hang up his deerstalker but need to have a conversation about where the story can go.
He told Radio Times: "Right at this moment, we really don't know about the future.
"Mark and I have to have a long chat, possibly on a train, about what we'd actually do with another run.
"We love the show very much, and that means we don't want to let go of it before we have to."
Sherlock has been a ratings hit for the BBC and Moffat said everybody involved with the programme knows how special it is.
But he added: "At the same time, because we love Sherlock the way we do, we don't want to keep it going past its natural term."
Moffat said the team had been unsure there would be a fourth run until ideas started to flow and said they have to be that "excited" again before committing to another season.
He said: "So give us a moment and Mark and I will go back to (Arthur Conan) Doyle and see what we've missed. The game may still be on.
"Unless, of course, everybody dies at the end of series four."
The new three-part series of Sherlock started on New Year's Day and saw Mary Watson (Amanda Abbington) shot dead as she jumped in front of a bullet intended for Sherlock.
The series concludes on Sunday.