Blue Bloods: Season 8, Episode 21

8 - 21: The Devil You Know

Frank goes head-to-head with a data-tracking company when they refuse to unlock the phone of a terrorist that may hold information regarding upcoming targets. Also, when Erin obtains information about an impending murder from a shady source, she gets Danny and Baez involved, despite the questionable agenda of the informant, and Jamie and Eddie try to locate a woman who kidnapped a newborn baby.