The day Ava Martin met John Watson they were both three years old and their parents had both sent them to the same nursery school.

Ava was playing with dolls by herself when a group of over exuberant boys began to hassle her, taking the dolls and holding them over her head and pulling her long red hair.

She started to cry and another boy, a sandy haired smaller boy, came over from the sandbox and pushed over the boy holding the doll. A scuffle broke out but was quickly dissolved by the teachers and the sandy haired boy was punished for starting the fight and not allowed to have a cookie at break time.

Ava thought he looked sad and he was made to sit by himself so she hid her own cookie and when break was over she went over to the sandbox and sat with him and shared the cookie. She would always remember the smile he gave her.

She knew they'd be friends.

...

They were both sixteen when Ava's mum died. She had been in a car accident. They remembered her laughing in the kitchen and fixing them snacks after school. Her dad pulled her out of class to tell her the news.

John didn't know what had happened until he went home that evening and his parents told him what happened. He hugged his mum tight knowing he was lucky to have her and then ran next door as fast as he could.

He spent the entire funeral holding her hand.

She knew he would always be there.

...

Ava was twenty seven when John called her to say he'd finished medical school. She went to his graduation and smiled the whole way through.

They went out to lunch afterwards and he told her he had joined the army. She cried that night but at the same time she understood. It was just so John to want to help the weak.

Ava was afraid he'd get hurt but she let him go and wished him luck.

She knew he'd be a hero.

...

She told John she was moving to Paris on his thirty second birthday. A big architecture company had offered her a job.

Ava expected him to be pleased but he was angry that she hadn't told him sooner and they had their first big fight. She called him a hypocrite because he'd signed up to the army without telling her.

They didn't speak for the next four years.

She knew he was angry but so was she.

...

It was her thirty fifth year when she got the phone call from John's sister Harry. She knew something was wrong the minute she answered because Ava had never spoken more than four polite words to John's elder sibling.

She caught the next flight to Heathrow and spent two days by John's bedside while he recovered from the bullet wound.

No apology was necessary, everything was forgotten the moment he opened his eyes and saw her holding his hand like he'd done at her mother's funeral.

Ava saw the dull look in his eyes and in the timbre of his voice whenever they spoke or saw each other for the next year.

She knew he needed adventure.

...

When she first heard the name Sherlock Holmes it was a week from her thirty sixth birthday. John called her while she was working on a new design. She put down her pad the moment he started speaking.

Ava sat and listened to his excitement and his story. Detectives, murders and cab drivers. She wasn't sure whether to laugh or tell him off for shooting a man. She settled for both and swore a lot, mostly in French, but when she went to bed that evening she was smiling.

She knew he'd found what he needed.

...

It was only one and a half years later when she read the news in the paper. The months had flown by in a whirlwind of blog reports, a media frenzy, lots and lots of cases and at one point an imaginary dog.

Then he stopped writing his blog and he stopped calling. Ava booked herself on the next flight to Heathrow and took a cab to 221B Baker Street.

The landlady Mrs Hudson told her John was refusing to leave the flat and wouldn't let anyone in. Ava banged on the door for five minutes and begged, pleaded, argued and eventually blackmailed her way inside.

Her friend was sitting on his sofa with the curtains drawn and she recognised the behaviour he was exhibiting as his grieving process. He'd done the same thing when Ava's mum had died and when his dog had died a year later.

John liked to shut himself away from the world so he didn't have to pretend to be getting better. He didn't want people to see.

She refused to allow him to do this again and flung open the curtains to let sunshine in. She ignored the baelful glare from the man on the sofa and proceeded to clean up the flat before finally rounding on him.

After many threats of dragging him outside in his pyjamas and calling him Johnathon he finally conceded to taking a shower and getting dressed.

Ava watched him try to get better for her; she had never seen anyone try as hard to act as though he was becoming better, as though he was happy.

She hid her engagement ring. She didn't want him to have to try any harder.

She knew he was broken.

...

After three days with no change she'd had enough and begged him to come back to France with her, to go somewhere he wouldn't be reminded of him every time he went somewhere. Every room in that flat had memories, every time he took a cab or saw a familiar street.

John refused and she went home alone. She called him every day but nothing changed.

It only took another week before he turned up on her doorstep to ask to stay and another three before some light returned to his eyes. Her fiancée stayed with a friend per her request.

She did tell John eventually and he was genuinely happy for her and told her she was probably right to wait. She gave him a hug before he got on the plane back home.

She knew he'd be ok eventually.

...

He came to her wedding when they were both thirty eight. He walked her down the aisle because her father had passed away.

She could have sworn he had tears in his eyes when she said her vows. He danced and laughed and she could see he was much happier than before. He made friends with Dean her new husband and Ava was glad.

She knew he'd begun to heal.

...

When Ava got the call the day after her thirty ninth birthday that Sherlock Holmes was still alive she'd dropped her cup of coffee in the street and sworn loudly in French.

She told John to punch him in the face and he told her he had. He was angry and hurt that he'd been lied to but he'd calmed down slightly when he'd been told the reason for the deception.

Ava still called him every name under the sun and John still hadn't forgiven him.

She knew he would though.

...

John called Ava when they were both forty. He had never been more scared in his life than to tell his friend of thirty seven years that he was now dating the madman that had faked this own death.

When he'd finally stuttered out the impossible words and told her he loved him he heard her laugh. Then he heard her say two words that had him gaping like a fish.

"I know."