Colleen O'Brien's Apartment was the apartment that Peggy Carter shared with Colleen O'Brien. Carter abandoned it following O'Brien's death.
History
A Day of Work
Peggy Carter prepared herself for another day of work for the Strategic Scientific Reserve, checking the newspaper to read about Howard Stark's Senate hearings concerning the sale of his weapons in the black market. Carter drank a cup of tea, prepared her clothes and watered the plants in the apartment.
As Carter was about to close her bed, Colleen O'Brien, Carter's roommate, arrived from her job at a factory, complaining how ten women were released to be replaced by returning World War II veterans, even though the veterans were not experienced with the factory's work, as O'Brien had to explain to one of the veterans how to use a rivet gun.
Carter listened as she finished grabbing her things, returning O'Brien a blouse she took the night before. O'Brien taunted Carter once again with her reluctance to go on dates with men, explaining that there was difference between being an independent woman and a spinster.
Carter dismissed the topic telling her to rest for the rest of the day, given that O'Brien was feeling sick, even thinking she had tuberculosis. Before Carter left, O'Brien reminded her that she would go to the cinema with her friends the following Saturday, and wanted Carter to accompany her.
Carter said she would try, but could not assure she would be free, as her work for the New York Bell Company, the cover used by the Strategic Scientific Reserve, kept her very busy. O'Brien was confounded that a job at a phone company was so important, even a matter of "life and death", to which Carter replied she had no idea.[1]
Neutralizing the Nitramene
Peggy Carter returned to her apartment, finding that her roommate Colleen O'Brien was inside instead of being at work as Carter expected. O'Brien explained that she was sent home due to having fever, and though she offered to give the bed to Carter as part of their agreement to share the bed, Carter refused and offered to make tea.
O'Brien realized that Carter was wearing a night dress, complimenting her appearance, and asked if she had gone out on a date. Carter told her she went, at least in a manner of speaking. O'Brien was proud of Carter, knowing that she was a woman deserving not to be alone and asked to tell her every detail the following morning.
Carter entered the bathroom to prepare a solution of sodium hydrogen carbonate and acetate using a combination of baking soda and vinegar, in order to neutralize the Nitramene sample that she stole from Spider Raymond. Carter carefully extracted the core of the device and sprayed it with the solution, effectively neutralizing the Nitramene.
However, just as Carter was about to have a drink to celebrate her success, she heard a noise coming from the bedroom, and quickly went to investigate what happened. Carter found the room had been searched, and when she approached O'Brien at the bed, she found her dead body with a shot in her forehead.
The man in the Green Suit that was at La Martinique emerged from the wardrobe, trying to shoot Carter and recover the Nitramene, but she managed to defend herself from him. During the fight, Carter saw a peculiar scar in the man's throat, and ended up throwing him through the window; the man was able to get up and escape.
Carter went on to check her friend's dead body and started to cry over her loss.[1]