Iron Man, Vol. 4 #22 (2007)

Haunted, Part 2
Stark continues to investigate Gadget's death, and is forced to shut down the Nebraska Initiative to get the job done. Graviton is acting rather crazy, but tips off Stark to hallucinations of the dead that they both share. The Mandarin, meanwhile, is working with the Secretary of Defense (under a false I.D.) to develop Extremis into a new Captain America by the end of the year. Finally, Stark realizes that it was actually Gadget's partner from the Initiative that killed her, though he hasn't deciphered the motive.
Release Date: 2007