The firehouse gets a new chief (Jerry Adler), who is rumored to possess a very special gift; Tommy suffers embarrassment during a hockey game against the NYPD; Franco works up the nerve to propose to Natalie while Sean tries to talk Maggie out of a divorce; and Sheila makes a surprising proposition as Janet's depression deepens.

Tommy and Janet deal with revelations about the baby; Sean learns a secret that Mike has been trying to hide; the new probie holds the guys to thier agreement about doing no 'probie' work; and lou's cousin Mike visits.

A devastating fire has a profound effect on the crew; Tommy wrestles with his feelings about the baby; Alicia (Susan Sarandon) returns with a proposition for Franco; Troy breaks up with Sheila while Lou makes a tough decision about Theresa; and Sean apologizes to Mike about the fire he set that burned down Mike's mother's house.

Janet plots revenge when she learns what Tommy did with the baby; Franco questions his marriage proposal to Natalie in light of Alicia and Keela's return; and Tommy faces his ghosts.

The Gavin clan stages an intervention after several disturbing family calls; the mysterious woman (Gina Gershon) from the restaurant leaves Tommy wanting more; Janet must take matters into her own hands to get her baby back; and a depressed Mike calls Tommy in a moment of despair

The Gavin family AA group's first meeting doesn't go exactly as planned. Tommy bribes Colleen for information on Janet. Franco learns the truth about Natalie from Richie while Lou contemplates revenge on Cousin Mike.

In the fourth-season finale, Sheila learns that Jimmy's ghost has been spotted on several occasions, so she investigates. Meanwhile, Colleen blames Tommy for her failed relationship; Franco and Natalie come to an understanding, as do Lou, Cousin Mike and Latrina; and Tommy spends time with his father.

Tommy copes with the loss of his father and a new man in Janet's life. Sheila finds a different way to deal with her issues while Sean, Franco, and Mike concoct a surefire way to get rich and laid.

An exotic visitor sparks mixed reactions in the firehouse. Tommy deals with the possibility of expulsion from the FDNY and a new sponsorship role in AA. As Mike and the guys renovate their new bar, Sheila learns that being a big sister isn't always easy.

The calls from Tommy's AA sponsee increase as Tommy attempts to navigate a touchy issue with Colleen. Genvieve's interviews spark controversial viewpoints in the firehouse concerning the political and religious implications of 9/11-viewpoints which Mike will not tolerate.

A personal milestone finds Tommy back at Ground Zero. Genevieve's perspective on 9/11 incenses Tommy, whereas Franco's point of view has more dire consequences. Meanwhile, Sean's back pain turns out to be more serious than he had expected and the success of Mike's bar becomes a handful.

A late-night cleanup turns into a nightmare for Tommy when several unexpected visitors stop by the bar. Feinberg allows Damien to ride along with the crew, but may not be prepared for the consequences.

Tension runs high as Needles holds the guys accountable for their lack of judgment. Tommy steps up and takes responsibility for Damian's future in the firehouse. Sheila provides Tommy with an oasis as a sign of her gratitude but it may not be enough to save him from the wrath of Mike, Dwight, and the ghosts of Tommy's past.

The guys visit Sean in the hospital; Katy is home from school and wants a family dinner---one that includes Colleen and Black Shawn; and Lou and Tommy make a wager concerning the women in their lives.

Franco has his first FDNY-tournament fight, and he and Carla (Tawny Cypress) have an encounter outside the gym; Candy cooks dinner for Lou; the guys have a surprise for Sean when they visit him in the hospital, and he has one for them. The guys also plan an outing for the kids in the cancer ward.

The perfect party becomes a nightmare when a herd of brutish women infiltrate the bar. Tommy's love triangle reaches new heights.

Damian receives an offer that unsettles Tommy; Lou discusses his upcoming wedding plans with Tommy and Needles.

Franco steps into the ring with one of Carla's friends;Tommy tends bar after a failed rescue leaves the crew in the dumps.

A terrifying vision of the afterlife leaves Tommy shaken as he attempts to reconnect with his friends and family back on the outside. At the firehouse, the crew’s fate hangs in the balance when the department decides to cut costs.

With Damian confined to a chair and a new baby on the way, Sheila and Janet join forces and shake-up Tommy’s family life.