The envelopes were TARDIS blue with numbers ranging from one to five on them. Each went to a different time or place connecting a specific group of people. A specific group of people that were only connected by one man, The Doctor.

...

One

John Watson arrived home from his shift at the hospital to a blue envelope on his door step. He picked it up and spun it in his fingers before fishing for his key, a smile forming on his face.

Sherlock Holmes was pacing back and forth across the flat, newspaper clippings were placed haphazardly along the wall above the fireplace. He'd been trying to crack this case for nearly three days and it was putting him on edge.

"Sherlock!" John called as he entered the apartment, "look what came".

Sherlock was across the room in a flash as he took the envelope from John's hands.

"It seems our old friend The Doctor has a message for us" he said.

"Just open it already".

The message on the piece of TARDIS blue paper was simple.

Dear Sherlock and John,

I've decided that it's time for a party!
I hope you'd like to join me. There'll be
other friends there that I'm hoping you
could meet.

The Doctor

...

Two

"Clara!" Angie yelled, running in from outside "there's a letter for you".

Clara smiled at the girl and took the letter from her hands. She knew immediately who it was from. She ran her fingers absentmindedly over the envelope before opening it gently.

My Dear Clara,

I'm having a party! You must join
me. Also, what do people do at
parties? I'm a little out of practice
and may need your help.

The Doctor

Oh Doctor...

...

Three

"Dean that's your third pie" Sam didn't even look up at his brother.

"Shut up, Sammy" Dean muttered; mouth full.

A letter was slid under the motel door. A letter in a bright blue envelope.

Sam got up and went to pick up the letter as Dean put his pie down.

"A message from The Doctor" Sam looked at the envelope.

"I wonder what it is this time".

"An invitation".

Sam and Dean,

It's time we caught up. If you're
not too busy fighting vampires and
ghosts then maybe you could come
to my party. It's going to be cool.
Because party's are cool.

The Doctor

The faint sound of a flutter of wings could be heard and Dean caught a glimpse of a beige trench coat out of the corner of his eyes.

"Hello Dean. Sam".

"Oh. Hi Cas".

"I see you got one as well" and in his hands was another blue envelope. "I am not sure how The Doctor managed it. I did not know that letters could be received in heaven".

"The Doctor can make anything happen if he wants it to".

"You should come with us" Sam smiled.

"I..".

"No, Cas, you should definitely come with us".

"I guess I could... consider the thought".

"Cas" Dean smirked "you gotta live a little".

...

Four

It had been a month and a half since New York and the Avengers were sitting around S.H.I.E.L.D with the feeling of accomplishment still in their systems. Though the feel of loss was strong as well.

Tony and Bruce were sitting around discussing the alien technology that had been used during New York. Steve was staring at Coulson's playing cards with the same level of sadness as he had so many times before. And Natasha and Clint were tossing obvious innuendos back and forth, something about Budapest again. Thor hadn't returned since taking his brother back to Asgard with him.

An agent approached the group with an unmistakable blue envelope. The group leaned closer together as Tony clasped the envelope in his hands.

"From The Doctor" Steve said quietly.

"I wonder what it is this time" Tony sat back, passing the envelope to Bruce.

Bruce opened the envelope and set the letter down on the table so everyone could read it.

Avengers Assemble!

That was clever wasn't it? I could be clever.
I'm having a party and I would
like all of you to come along. It might
be a good distraction as well considering
the events in New York. Unless that
hasn't happened yet...

The Doctor

...

Five

Merlin walked into the King and Queen's chambers without knocking. He had a blue envelope in his hands that could only mean one thing and he was incredibly excited to share the news.

King Arthur called a meeting of his most trusted knights: Gwaine, Lancelot, Percival, Leon and Elyan.

"It seems we have received some sort of letter" Arthur began. "From The Doctor".

A hush seemed to fall over the room, more shocked than anything. They didn't think they would hear from The Doctor again. Especially after last time.

"It seems to be an invitation to some sort of party. It's addressed to all of us and I believe that we should all attend. It would seem rude not to and The Doctor is someone that seems to be a strong ally to have".

Prince Arthur and Queen Gweivere of Camelot,
their most trusted knights and Merlin,

It's been too long. Arthur I've heard that
you've grown into the king you were always
destined to be. Merlin, good job. I'm having
a party and I hope to see all of you there.

The Doctor

...

One

"This is ridiculous John, why do I have to hold this... thing".

"Sherlock, it's just a balloon. It's a gift. The Doctor will love it. And he'll love it even more if you're the one who gives it to him" John hid his smirk as he slid on his jacket.

"It seems... pointless".

"It's a gift, Sherlock. To thank him for having us".

"He has enough room in that monstrous blue box of his. Surely we don't have to thank him for having us".

"Sherlock" John sighed. "Just carry the damn balloon will you".

And with that they left 221B.

...

Two

"Doctor!?" Clara called to the clouds, cup of tea in hand. People were staring at her and she laughed, waiting for it to quieten down a bit. She didn't want anyone seeing what she was about to do.

Clara jumped and grabbed at the end of the ladder into the clouds. She couldn't wait to see her doctor again.

...

Three

"I am NOT going up there" Dean crossed his arms across his chest.

"Come on Dean, it's not that bad".

"I think this is more Cas' thing".

"Dean, I promise you that you won't fall. I will fly up beside you. It will be fine".

The flapping of wings was heard.

"Well isn't this a sight to see". A short man, well short compared to the Winchesters, in a dark suit, smirked.

"Crowley?".

"It's good to see you too boys".

"What are you doing here?" Sam questioned.

"Well, I can't miss out on all the fun can I, moose?".

"Please Dean".

"No, Cas, I'm not going up there".

"It will be fine".

There was another flutter of wings.

"Well if you two have stopped fighting like an old married couple I guess we should start up". Another short man appeared.

"Oh great, anyone else coming will you, Gabriel?".

"Dean, Dean, Dean. You haven't changed at all have you".

"Well I'm going up first so you better sort this all out among yourselves" Crowley laughed, starting to climb the ladder to the stairs.

"Cas...".

"I will be right here Dean and Sam will be right behind you".

"You'll be fine, Dean, seriously" Sam smirked.

Dean groaned and started up the ladder as Cas and Gabriel's wings appeared and they started to fly up towards the clouds.

"I'm right behind you, Dean" Sam reassured.

Once on the staircase Cas gripped Dean's hand in his and Sam kept a firm hand on his back, his other holding tightly to the present under his arm. Dean was fine... except for the taunts of Crowley and Gabriel, but he tried his best to block them out and focus on not falling to his death.

...

Four

"Well this is interesting isn't it" Tony stared up at the staircase above them.

"It's very Doctorish" Steve added.

"Definitely" Bruce smiled faintly.

"Well, are we gonna go up then?" Clint asked.

"Well... I'm gonna fly up" Tony smirked. "Jarvis?" and then he was disappearing into the clouds.

Steve climbed up first, watching Tony through still amazed eyes.

Then Clint and Natasha, striking up a deep conversation about Budapest once again.

Bruce climbed up last. Fixing his glasses and looking around at the clouds. Feeling happier than he thought he's ever been.

...

Five

"Merlin this is utterly ridiculos. It should be impossible to go into the clouds" Arthur glared up at the staircase.

"Arthur, after everything you've seen, this can't be such a surprise" Gwen smiled fondly, placing a light hand on his arm.

"I think it's gonna be fantastic" Gwaine smiled. He could sense the adventure.

Lancelot handed the flaming torch over to Arthur as the knights prepared for the ascent into the clouds.

Gwen went up first, pointing to the clouds and talking animatedly to her husband and friends.

Arthur followed close behind, Merlin on his heels with his dragon Aithusa flying along beside him.

The knights then followed quickly, excitement brewing within them.

...

One

"Sherlock! John! It's so great to see you both" The Doctor came out of the TARDIS beaming, it seemed, brighter than the last time they had seen him.

"It's great to see you too, Doctor" John smiled, accepting the large bear hug that he and Sherlock found themselves in. Sherlock was never impressed with the hugs.

"It's been a while" Sherlock added, fixing his coat for something to do, while still keeping a hold on the disastrous balloon.

"Is that a balloon? Balloons are cool".

"You can take it if you want" Sherlock held the balloon out.

"Not yet, I have a job for you".

The Doctor disappeared into the TARDIS and then came out with a sign that read:

"No Admittance

Except on Party Business"

John hammered the sign into the cloud floor while Sherlock stood next to him, balloon still in his hand and unimpressed expression gracing his face.

...