Moffat told Vulture: “She’s developed hugely. She wasn’t even meant to come back after her first appearance, but she worked so well. Louise Brealey was so good. The girl with the unrequited crush became the first person to make Sherlock apologize in ‘A Scandal in Belgravia,’ and then you see it really shift around.”

The ‘His Last Vow’ writer explained: “Whereas all of Sherlock’s emotion on the rooftop when he’s talking to John in ‘The Reichenbach Fall’ is completely faked — he’s just trying to give his friend a bad time so he’ll be in an emotional state to believe what’s about to happen — the emotion when Sherlock turns up to Molly in that episode and says ‘I need you,’ I mean, it’s amazing everyone didn’t just get it right there. For God’s sake, what do you think he’s thinking about? He’s gone to a woman who works in a morgue — what do you think happens next?”

He added: “So she’s become one of a very small select band of people he absolutely trusts. And he adores Molly, of course he does. He loves her. I don’t think she has the same sort of crush on him anymore. She’s fascinated by him, but she knows that’s not who she actually wants to end up with. She properly cares about him — and gets angry at him, and tells him off. It’s revealing that she’s in his mind palace. She’s one of the people he keeps himself up to the mark with.”

> Find out everything we know so far about Series 4 in our news summary.

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Watch the Series 3 teaser trailer…