The CBS crime drama follows Det. Carrie Wells (Montgomery), a cop who has perfect recall of her entire life, expect for the day her sister was murdered.
© CBS
"I know nothing about what actually happened, who did it or why," the actress revealed to Digital Spy. "It's better for me acting-wise in a lot of ways not to know.
"She's on this mission to solve her sister's murder and for whatever reason solving the other cases keeps bringing back pieces of [her memory of that day]."
Montgomery - who previously starred in CBS series Without a Trace - added that she has "fun" playing "imaginary cops".
"Samantha Spade on Without A Trace was much more by the book and impressionable," she said. "This character's a lot more action-based and renegade and she doesn't wear suits and she doesn't dress like a cop and she doesn't act like a cop.
"Carrie doesn't care - she does her own thing and she'll do whatever it takes to solve a case, whether it's okay and by the book or not. That's kind of a cool thing to do - I like that."
Unforgettable was briefly cancelled by CBS, but later received a second season pick-up for 2013.
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Watch a recap of Unforgettable's first season below:
