If I had Written Iron Man 3, Here is the story-line I would have done. It would have made more sense than a phony Mandarin or A.I.M. It would have been a "Revenge of Justin Hammer" Story.
In the beginning I would have Hammer dressed in a suit and out of his prison grays being escorted by S.H.I.E.L.D. agents to a nondescript facility. Inside they bring him to small interrogation room. In the room are Senator Stern and Killian The Head of A.I.M.
Senator Stern would inform Hammer that he was being released on his recognizance provided he help Killian do one thing... Destroy Stark's reputation as a hero.
Hammer would ask Stern if they were S.H.I.E.L.D. Agents or something and Stern would reply "Something like that."
A few days later we see Tony Stark (in his Iron Man suit) at a ceremony at the U.N. Stark is posing for pictures with the Ambassador of Wakanda (who is a big fan of Iron Man.)
As Iron Man is standing with the Ambassador (with his hand on the man's back) his repulsor suddenly fires- Tearing through the chest of the Wakandan Ambassador!
The crowd stands stunned, having just witness a murder.
Tony Stark is surrounded by security and police and immediately surrenders to authorities- He takes off his helmet, his face shocked and stunned, getting down on his knees, he puts his hands on the ground. Stark is arrested but released on Bail by his Attorney Jennifer Walters (wink.) It is determined to be an accidental misfire and murder charges are dropped, but the media is going berserk.
A few days later at a congressional hearing. Stark is told to turn over his suit- All of his Suits to S.H.I.E.L.D.
Nick Fury is present to take possession of the Suits. Stark pleads with Fury to help him find out who's responsible for hacking into his suit. Rhodey also turns in his (Iron Patriot) suit and vows to help Tony get whoever is behind this.
Now Suit-less and vulnerable. Tony shows up at the Gym where Steve Rogers works out on the heavy bag. He pleads with Cap to show him some moves and that he is going on a mission to find out who's behind the suit hacking. Cap agrees to help and there is a montage of Cap showing Tony Combat Karate, Krav Maga and a few other deadly fighting moves.
After a few days of training with Steve Rogers, Tony and Rhodey are ready to go to Monaco, where Jarvis has narrowed the signal origination. Steve tells them he can't go and that he's under orders (from S.H.I.E.L.D.) to not even be talking to Stark right now. Tony thanks him anyway and is off to Monaco.
Want to read more? Stay tuned for part 2 of this Iron Man 3: Retconned!