A good Samaritan with a police record takes action against a terrorizing subway criminal, forcing the Reagans to weigh the rights and wrongs of vigilantism.

Danny, Erin and Frank work together to seek justice when the main suspect in a rape case is protected by diplomatic immunity.

The entire NYPD is mobilized to find the killer of an off-duty police officer murdered during a diamond heist.

The Reagans argue the advantages and disadvantages of profiling; Danny, Frank and the rest of the NYPD search for a homemade bomb about to detonate in the city.

Danny tries to find the source of a deadly narcotic after three teenagers die from an overdose.

When Erin tries to take down a gang leader using his law-abiding brother as bait, the family debates her methods.

After meeting with federal agents in a dark edge of Chinatown, Jamie witnesses a crime in progress and his suspect is killed while in pursuit. Now, Danny must solve the case in order for Jamie to avoid an Internal Affairs investigation.

The life of a Reagan is put in danger when three dangerous criminals are released from prison.

Danny investigates when a doorman at a nightclub is murdered; Frank makes a decision about a former partner's future.

A high-end escort's body is found in the river; Frank vows to get justice in a 25-year-old case.

Danny must delve into the family politics of the Russian mob while investigating the death of a gangster's son; Erin becomes involved in a high-profile corruption case.

Danny investigates the shooting of an undercover counter-terrorism agent who was involved with infiltrating a sleeper cell.

When a girl is kidnapped, Jackie and Danny suspect her drug-addicted boyfriend is responsible; Erin's relationship with her boss takes a step forward.

When an assassination attempt is made on Frank's life, Danny goes on a hunt to track down the shooter and find out if the attack was random or by someone with a vendetta against the Commissioner.

When an unidentified young girl is found murdered at a debutante ball, Danny and Jackie look to the prostitute found giving her a hard time on the hotel's surveillance camera for clues. Meanwhile, Nicky gets a glimpse of her first murder victim as she rides along with Danny when he gets the call to investigate.

When a former U.S. Marine and war hero-turned-homeless man is found murdered, Danny, a former Marine himself, feels a personal connection and is determined to find the killer. Meanwhile, erroneous information about Frank running for mayor is leaked to the press.

Just before Danny is to give witness testimony at a Peruvian drug lord's murder trial, Linda is kidnapped. This drug lord has a history of intimidating witnesses.

Danny and Jackie investigate the cut-throat world of fashion after Linda's runway model niece and a reporter are poisoned at a fashion show.

Frank's frustrations rise when the media sensationalizes the murder of a tourist shot and killed outside a trendy Lower East Side restaurant.

Neighbors of the Reagans are murdered and their son becomes the prime suspect. Jamie is convinced he's being pursued by the Blue Templar when his gun goes missing.

In his attempt to expose the Blue Templar, Frank chooses to bypass Internal Affairs after a drug bust indicates dirty cops are involved.