The Black Knight
Tony Stark suffers another attack on his heart just as the Black Knight arrives to trash Stark's factory and draw out Iron Man, since he wants revenge on the Avengers. Tony locks himself in his office, quickly adding on extra energy packs to the Iron Man armor in order to sustain his heart.
Pepper and Happy, concerned for their sickly boss, attempt to break into Tony's office while Iron Man does battle with the Black Knight, until Happy becomes a target himself.
Eventually Iron Man defeats the Black Knight by flipping over his horse's hooves, making the Black Knight fall to the ground, almost dying.
Worst of all, Tony discovers that his body now relies on the full suit of armor, not just the chest-plate, to keep him alive. Meaning that he must now wear the iron suit full-time, or die.
What starts as a quiet evening on watch for Captain America turns into an all out brawl as a group of thieves with lofty ambitions break into the Avengers Mansion. However, even though they manage to tie him up and leave him seemingly helpless, Captain America shows them why he is such a good hand-to-hand fighter. He is able to defeat Bull Brogin and his gang, all by himself.