Dear Nincompoop,
Mycroft has a girlfriend.
She's called Penelope, and is incredibly posh.
This is Penelope:

Mycroft has had some really weird girlfriends before. Such as this girl who called herself Raven Princess.

And then there was Charlie, who could have been a man, but we're not sure.

Mum and Dad love Penelope. They say she might be The One. But they said that about Charlie. And Raven Princess.
Me and Watson don't like Penelope. She's stuck up, and says that she knows Mycroft through work. Although, thinking about it, he might work for her.
After school today, Angie and Diesel came round. That was when we found out about Penelope and Mycroft. Dad was like, "Hey guys! This is Penelope! She's Mycroft's new girlfriend!"
And we all looked at her. She looked back at us and stood up.
"Salutations. My name is Penelope." she said, in some really posh voice.
"Salutations to you too." I replied.
"You need elocution lessons. Mummy and Daddy have sent me to them since I was five, so I can learn to speak properly, unlike the common people."
For some reason, Angie found it really funny when she said "Mummy and Daddy." Watson did too.
Diesel, however, decided to talk, which is rare for him.
"Gawdon Bennet! Hello ter yew an' all, Penelope. Me an' me friends 'ave just come 'ome from school, an' it's nice ter meet you. OK?" he said, in a perfect Cockney accent.
And she just looked at us in disgust. It was priceless.
Mum and Dad shooed us away, telling us that Penelope was Very Important to Mycroft, and that he was Happier Than He Normally Was, and that we Shouldn't Ruin Moments Like This, nor Tease People Because Of The Way They Speak.
I'm feeling a bit peckish, so I'm going to get something to eat.
Later...Me and Watson have just found out that Penelope is staying the night. So that means that I have to sleep in Watson's room on the floor. I'm not happy about this.
I mean, I don't mind sharing with Watson, as we get on quite well, but I do mind that Penelope being in
my room with
my stuff. I bet you anything that something is going to be broken tomorrow.
What is she sleepwalks?
What if she snores?
What if she wants revenge over what Diesel did?
Why is she even sleeping at our place anyway? From what we've heard, she lives in a manor house down the road, and has five bedrooms to herself. She doesn't need to sleep here.
Therefore, I have decided that there's a mystery that needs solving. I live up to my name, and love mysteries.
Well, unless it involves Penelope sleeping in my room.
Watson also loves them, and serves as my sidekick. So we've decided to work out what is going on.
He's looking around for clues, like any good sidekick does. Meanwhile, I'm thinking of all the possibilities. So far, I have a list of posibilites.
1. She loves Mycroft so much she can't be in a different building from him.
2. She's planning on murdering me and Watson after what Diesel did to her.
3. She's trying to manipulate my parents into liking her, so she can marry Mycroft and then kidnap him.
4. She's lazy and can't be bothered to go home.
5. Something fishy is going on at her house and she's staying here.
6. She works for a top secret organization and there's a plan involving us and something else.
7. She wants to make us breakfast tomorrow, so she's staying and planning on working on it through night.
Number seven seems unlikely, but I have to think of everything.
Watson's just came back, and he's found Mycroft's journal.
"We could find out how he met her." he suggested.
Brilliant. Except...
Mycroft's journal has a lock.
Me and Watson never got a lock for
OUR journals.
"You need to crack the code, Sherlock. And reasonably fast, or Mycroft will notice." Watson said.
As if I didn't know already?
So, nincompoop, I'm going to try and work out this code, so we can get on with this mystery.
Sincerely,
Sherlock.