Synopsis
Tony Stark continues to spend his time tinkering, and romancing the ladies. This time he combines both as he soups up a girlfriend's sports car. Unfortunately he's got the girls mixed up, as this one isn't the expert driver.
CEO Pepper Potts isn't impressed by this. Nor with the current state of the JARVIS AI, now embedded in the Iron Man armour. Tony says this ongoing project has reached the equivalent of the teenage phase, and it's getting stroppy.
Pepper seems more cool about Tony personally seeking out Extremis users now. The 3rd of the 4 detected sites is a group of 13 in Paris, who don't seem to be moving much. He's going after that group now, and to face 13 Extremis-amplified beings he's opting for strength and fire-power in his modular armour. Pepper asks if this is a new version of War Machine, but Tony replies that he's not letting the government have any of this new tech.
In Paris, Iron Man enters the catacombs. As to be expected he sees skulls embedded in the walls. But he didn't expect them to be incised with rune-like letters. Nor did he expect to sense a sophisticated security system. Patching into the system and using its cameras he sees a heavily-armed and weary scientist, hints of body parts, and lots of blood. And 13 white-haired pointy-toothed women, also decorated with runes.
They are sat still before a doorway in a wall also covered in runes. As Iron Man approaches closer, they sense him and attack with serpentine hisses. Extremis has made them super-strong. Using his repulsor power to generate a force field, Tony holds them off long enough to get through the doorway. And the women return to watching and waiting.
The scientist is inside the room, and he tells Stark that the runes will keep the women out. He also explains what's going on.
The man and his associates had been trying to incarnate a cosmic being known as the Great Black Infinite into a human body by letting him impregnate a woman. But all the women they tried had died. So they acquired Extremis to create women strong enough in body for the job. To also stop them from going mad, these potential mothers were rendered mindless.
Despite this they could still recognise the runes. And their programming stops them from passing the runes around the door. As the skull-runes Iron Man passed on the way in stop them from escaping.
Expecting possible trouble the cult had armed themselves with high-tech weapons. But they hadn't been enough against their enhanced subjects. And all the other 'scientists' are now dead.
The Extremis source is in the room with them, and Iron Man makes a move to destroy it. The cultist shoots at him. The shell has no effect on Stark's armour, but it ricochets and blasts a hole in a wall. This hole isn't protected by runes. One of the demon women enters that way and tears their maker apart.
Iron Man destroys the sample of Extremis as the rest of the women enter and prepare to attack. But Stark instructs JARVIS to project a laser hologram of the guarding runes around him. And the women fall back into stasis.
Tony knows if he tries to leave they'll kill him before he can get to a warded exit. If he tries to blast a hole directly up to the surface, they'll be able to follow him out and go on a killing spree. So he programs his suit to shoot their heads off one by one. And closes his eyes so he doesn't have to watch.
But a body count only tallies 12 of them. Exiting the room he finds one woman who appears not to have moved during the whole incident. He can't justify killing her if she's not actively dangerous.
Next thing we see, Tony's back home and the demon woman is in the Raft supervillain prison, psychiatric wing. But she's pregnant, presumably with the child of the Great Black Infinite. And looking like this is what she planned.