So, like many Loki fans, I feel that Thor: Ragnarok made Loki seem a bit weak. Thor too. If you don't feel this, you will still love this. They are my favorite characters, so while I will include most of the original Avengers, they will be my focus. Spiderman, Falcon, and any others that have joined will not be in this story if they were not in The Avengers. Much love, but I don't know them (nor love them) well enough to write them. :)
I am a fan of the old Marvel movies: Thor, The Avengers, and Thor 2 was pretty good. I like almost all of the Avengers, but I am not a fan of Hawkeye and Black Widow simply because I am a fan of Loki and they were not very nice to him. (No one was, but they were the worst to him. And btw, I DO know he was trying to take over earth, lol)
Anyway, this story is going to be at the start of Thor: The Dark World and create Avengers 2. Loki has been put in prison, defiant as ever. Frigga has been killed by Elves, but they were neutralized by Thor quickly. Then several months later (7-8), Thor realizes something else has been going on between the realms and the Avengers assemble or whatever. Loki has taken Frigga's death very hard.
This is fanfiction and while they may not be this way now, how I write the characters is how I envision they should be. Characters will be similar to how they were in Avengers.
Please enjoy. And please review.

Frigga's death had taken its toll on Asgard. The realm had ceased its celebrations for the time being. It was quiet when they walked through the streets and although people still conversed and spent time with each other, their manner was quite subdued.

Prince Thor had stayed near his father's side through all of it, seeing as the realms were at peace.
His friends had often tried to get him to join them in their adventures. He had yielded a few times, but he preferred to remain in Asgard.

Today, however, was different. Heimdall had summoned him to the Bifrost. That's where he was headed now, hammer hanging form his hand.

Heimdall stared off the edge, sword gripped between his hands.

"You walk slowly these days, my prince." he said as Thor approached.

Thor laughed quietly at the ground "What words of wisdom do you have planned for me this day?"

"I have none to give. There is trouble elsewhere." Heimdall replied. Thor walked closer to him, face in a concerned frown.

"It seems that there have been numerous break throughs in the realms. Midgard has suffered the worst." Heimdall said, his voice as calm as ever.

"What kind of break throughs?" Thor asked, scowling.

"The Jotuns have found a way onto Midgard. I have seen only a few there and they returned back to Jotunheim quickly." Heimdall replied, yellow eyes reflecting the stars "They are quite restless. Thoughts of invasion have been spoken."

"Where is this entrance they have found?" Thor asked, hand tightening on the hammer "How is this possible?"

"I cannot see it." Heimdall said "It is shielded from my eyes. I recall the time your brother allowed Jotuns into Asgard. I could not see then either."

"Yes, but Loki is in prison. He has no power out here." Thor replied, waving a hand slightly.

"Loki is not behind this." Heimdall said "But like then, my eyes are shielded. Have you spoken to him lately?"

"No." Thor said "Odin spoke of isolation as part of his punishment."

Heimdall raised his chin "Your friends on Midgard. They have gathered, but I do not believe they know what has occurred."

Thor walked toward the edge of the Bifrost, staring down, almost as if he wished he could see "Where are they?"

"The city which the Chitari attacked." Heimdall replied.

"I must tell Odin of this." Thor said, turning.

"Wait. There have been others. I have seen the Chitari in Valaheim." Heimdall replied.

"Chitari? I thought they were all killed on Earth." Thor said with a frown.

Heimdall lifted up the sword and turned to the gold pedestal with a sigh "Many survived that battle. Valaheim has been able to fend off the few that have entered. I only tell you this as a warning."

"Are those the only realms?" Thor asked.

"Those are the ones that I have seen." Heimdall replied "Since I am blind to the portals, I will not know until they are within the realm."

"Where are the entrances they have found?" Odin asked, repeating his son's earlier question as he walked down the steps from his throne. After hearing the news, the king had ordered several guards to search the borders of Asgard for invaders.
Thor followed him as he walked down the hall "Heimdall cannot see them. I need to return to Earth to prevent any attacks from the Jotuns."

Odin stopped, staff grasped in his hand. He faced away from his son.

"Asgard is at peace." he said, looking up. He almost appeared to be talking to himself "The realms appear to to be safe. You may return to Earth." he turned to Thor "But if Jotunheim invades then you must come back and take more Asgardians with you. I do not want you to attempt to face them alone, no matter the support of Midgard. Lady Sif and the warriors will assist you if necessary."

"Thank you, father." Thor said. Odin had definitely grown older in the past months grieving for the queen. It was surprising that the Allfather had not objected to Thor's wishes. Many times he was not in his right mind.

The king picked up his staff and began walking down the hall towards his quarters. Thor turned back around to return to the Bifrost.