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Blue Bloods S8E21 — The Devil You Know
7.9
Blue Bloods•Season 8•Episode 21

The Devil You Know

7.9/10 · 409 votesMay 4, 201845 min

Ranked #10 of 22 in Season 8•matches the season avg

Discussion

Frank locks horns with a data-tracking company when they refuse to unlock a terrorist's phone that may hold information regarding upcoming targets. Erin obtains information about an impending murder from a shady source.

Directed byJohn Behring
Written byAllie Solomon
Previous episodeE20 · Your SixNext episodeE22 · My Aim is True
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Cast9

Tom Selleck

Tom Selleck

Frank Reagan

Donnie Wahlberg

Donnie Wahlberg

Danny Reagan

Bridget Moynahan

Bridget Moynahan

Erin Reagan-Boyle

Will Estes

Will Estes

Jamie Reagan

Len Cariou

Len Cariou

Henry Reagan

Vanessa Ray

Vanessa Ray

Eddie Janko

Abigail Hawk

Abigail Hawk

Abigail Baker

Marisa Ramirez

Marisa Ramirez

Maria Baez

Sami Gayle

Sami Gayle

Nicky Reagan-Boyle

Crew2

John Behring

John Behring

Director

Allie Solomon

Allie Solomon

Writer

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Episode Summary

"The Devil You Know" is episode 21 of Blue Bloods season 8. It scored 7.9/10 from 409 votes, ranking #10 of 22 episodes this season (season average 7.9). Directed by John Behring and written by Allie Solomon, it aired on May 4, 2018.

Next: E22 · My Aim is TrueBest of Season 8