Getting details about a new Sherlock season is like trying to solve an impossible crime: not easy.

STACK sat down with creators Steven Moffat and Mark Gatiss, producer Sue Vertue, and stars Benedict Cumberbatch and Amanda Abbington at Comic-Con to attempt to get even the smallest, spoiler-free morsel of what’s in store. Or at the very least, when we can expect to see the new series.

“We don’t actually know, “ says Moffat. “It’s true. I’m not holding out on you, we actually don’t know. We give it to the BBC and they do what they like with it.”

“The roads to wrath have demons beneath, and Sherlock’s have been waiting for a very long time,” offers Gatiss cryptically.

Even a jet-lagged Benedict Cumberbatch won’t let anything slip: “They did a series pitch the last time we filmed, so I had in the back of my mind a rough idea of where they want it to go.”

What we do know from the first Series 4 trailer, revealed at Comic-Con today, is that it’s due sometime in 2017, and looks darker and more sinister than previous seasons.

Gatiss confirms that this season, “particularly episode three, is the most like a Universal horror film with Basil Rathbone.”

Amanda Abbington, who plays Mary, adds that guest star Toby Jones is truly terrifying. “He frightened the bejesus out of us on set,” she says.

Sherlock did return in January with the special The Abominable Bride, but it’s been over two years since the last full season. And with both Martin Freeman and Benedict Cumberbatch now part of the Marvel universe, it’s getting harder to get them both together.

“It’s very difficult,” says Gatiss. “One of the great things about the job is it’s only every few years, so there’s room to do Doctor Strange and whatever in between and then come back to it. Both Martin and Benedict are very grateful for what the show has done for them, and hopefully we’ll carry on as long as we can.”