This is story related and can't be missed.
1: After locking the door and letting the cat in, the window is open.
2: Now climb through the window and exit through the next window.
3: Attempt to get past the bird and quickly grab the feather.
4: Exit the ledge to the right and go through the door to Nina's office.
5: Leave the office and use the elevator all the way to the right of the area.
6: Take the cavity magnetron out of the oven and leave through the window. Achievement unlocked:
7: Attempt to drop the cavitiy magnetron. Achievement unlocked:
8: Return to Nina's office and go through the portal. Achievement unlocked: