I just watched Iron Man 1&2 the other day. I'm new to the entire story.
In IM2 we learn that his blood is being poisoned and that he has tried every combination of every existing element as a cure - unsuccessfully. Then he deducts "the key" from the Expo park's plans which saves him.
What is that key? What element had he not tried?
I realize that the movie story has to be simplified, compared to the original story, so there are probably story elements that I have completely missed because they're only in the original works. We also saw that in LOTR.