A portal had been opened. Aliens had poured through it to attack. Manhattan had been decimated. All this, to be laid at the feet of one man - an Asgardian named Loki. The world had nearly been lost.
But it wasn't.
Earth had heroes to defend her in her time of need. Iron Man. Captain America. The Hulk. Hawkeye. Black Widow. Thor. The names were on every tongue after the disaster they resolved. Some people praised them... some cursed them. But all knew their names, and the name of the man responsible. Loki.
They took him prisoner, but without the bifrost Thor was unable to return the prisoner to the place that could best keep him under guard. The Realm Eternal. Asgard. Home. And so they had need to keep him safely locked away until a device could be constructed to use the Tesseract - that great and terrible source of power - to open a portal between Earth and Asgard. They had a need of something that could nullify his powers so that he may be contained. Something... or someone.
Quick Author's note: this takes place immediately after the avengers and may (probably will) encompass Ironman 3, Thor 2, Captain America 2, Agents of Shield and possibly even Avengers 2. I do not own the Avengers or any Marvel character.