Day 2: 6:00 A.M.-7:00 A.M. - S2-E23
Continuity mistake: When Kate Warner ascends the stairs in Kim Bauer bosses house, she holds her sunglasses in her left hand. When the camera changes she has sunglasses on her right hand and her left hand is empty.
Answer: According to Jack in season 5, Nina was "deep cover" before the pair ever met, so it's safe to assume she was recruited before she joined CTU. As for what her primary mission was, who knows? Perhaps it was to gather sensitive intel and pass it on to her superiors. Given that she worked for an intelligence agency, it's not a stretch. Or perhaps we may find out in season seven.
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