Things take a dangerous turn at the courthouse when Erin is taken hostage on Blue Bloods. "To Protect and Serve" is the third episode of the show's fourth season.
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Danny must keep it quiet when a movie star is shadowing him on the job on Blue Bloods. "The City That Never Sleeps" is the second episode of the show's fourth season.
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Blue Bloods has Marisa Ramirez as a full-time cast member. This is a photo from Season 4.
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Erin and Danny argue when she must release a suspect due to lack of evidence on the season premiere of Blue Bloods. "Unwritten Rules" is the first episode of the show's fourth season.
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Blue Bloods Season 4 Quotes

We decline to charge suspects every day. Many of them are guilty but you still need evidence.

Erin

Jamie: I thought I was just another cop.
Frank: You are. You're also a lawyer and you'll understand the why of this more than most.