Giggles floated down the stairs as Sherlock opened the front door. Giggles that were abruptly cut off with an "Oh, he's back" as he let it slam behind him and started up the stairs.

They hadn't forgotten. He'd assumed they would, what with Mary being a week late already.

'I didn't expect you to …' he started to say as he stepped into the living room but his words were lost, along with the breath in his lungs, when Archie barrelled into him and hugged him tightly, crying "Happy Birthday, Mr Holmes" at the same time. He couldn't quite bring himself to mind this form of greeting any more.

'We're getting some practice in,' Mary said from John's chair in answer to Sherlock's questioning glance. She looked tired, hands rubbing soothing circles over her bump, which was visibly moving, but was smiling widely all the same. 'Archie was quite excited when I told him we were coming to see you. Said you had a pair of putrefying lungs to show him.'

'Pictures of putrefying lungs,' Sherlock said, trying to disentangle himself. 'They're in the red file box under the desk.'

'Oh well, that makes it so much better.' John grinned at him from his perch next to Mary as Archie shot across the room. 'Will you be doing similar things with your godson when he's old enough?'

'Obviously. You've still not agreed on a name then?'

'No.' John shot him a rueful smile. 'I'm not going to name my son John, regardless of how persuasive both you and Mary try to be.'

'And as much as I love you, Dr Watson, I'm not having any child of mine spending his life as an Algernon, no matter that it was your Grandfather's name.'

'I should think not. And I don't understand your objection to …' Sherlock didn't get any further, as Mary firmly interrupted him.

'We haven't come to talk baby names, Sherlock. Or babies at all, for that matter.' Mary nudged John, who held out a small black box tied with silver ribbons. 'This is for you. Happy Birthday.'

Sherlock took it, somewhat hesitantly, and turned it once in his hands.

'Keys?' Sherlock couldn't keep the confusion out of his voice. 'Keys to what?'

'Just open it.' John fixed him with a hard stare that had his fingers undoing the ribbon and lifting the lid without any intervention from his brain.

Suddenly he found it very hard to breathe, because the brass key he tipped into the palm of his right hand had a small tag attached. The tag, in John's loopy scrawl, contained the words Watson Family Residence.

'… Because you are family,' John was saying, somewhere in front of him. 'Plus you helped us find the house in the first place and we've got keys for here. And I suspect you'll need to be coming to us for a while after little one finally makes an appearance, just until we've got used to having him in our lives.'

'Besides,' Mary chimed in, 'I really don't want you picking the lock every time you need to talk at John. You'll scratch the paintwork.'

'I …' Sherlock swallowed and tried again. 'I didn't think you'd want … A-are you sure?'

'We're sure.' They spoke together, exchanging smiles as they noticed.

'I don't know what to say,' Sherlock muttered, running his thumb over the cool metal.

'Your face is being quite eloquent as it is.' John reached out, grabbing the hand Sherlock had just dropped the box from and tugging him closer to them. 'But a simple thank you will do.'

'Yes, I …' Sherlock gave his head a brief shake, as if trying to wake himself, but his gaze remained transfixed on the key. 'Thank you. Both. Uh …'

'Sherlock!' Archie saved the need for more words by bounding back across the room and waving a photo under Sherlock's nose. 'Tell me why this one has green lumps.'

Sherlock blinked hard, closing his right hand tight round the key as he gentle wriggled his left out of John's grip and took the photo.

'Right, Archie.' Sherlock steered him back over to where he'd spread the photos over the rug. 'Do you remember what I said about …'

It didn't escape either John or Mary's notice that, as Sherlock sat down on the floor, now talking animatedly about lung tissue decomposition, he slipped the key into his left shirt pocket; right next to his heart.