I'm looking for a story but I remember very little about it, so any help is definitely appreciated. Could be Steve/Tony, Bucky/Tony or Steve/Tony/Bucky. I think Hydra or AIM are manufacturing stones that can open portals. I remember a scene where Tony is doing some kind of experiment on a stone and a bunch of scientists are scared, while Bruce is kind of resigned to Tony's antics.
I also remember a scene where Tony sort of falls through one of the portals and ends up in Dubai and Steve's also about to fall into one, but Bucky holds him with the mechanical arm. Oh, and Tony has to fly really fast from Dubai to the battle and it causes some problems with the arc reactor.
Ring any bells?