Tommy decides to make life a living hell for his wife's new boyfriend by wreaking havoc on his business and finances. Meanwhile, Chief Reilly faces possible suspension as the result of an altercation with a fellow firefighter and Lou decides to share his poetry.

A "friendly" date between Tommy and the widow of his dead cousin takes a unexpected turn when she makes a move on Tommy. Franco's ex-girlfriend shows up at the firehouse and claims he's the father of her five-year-old daughter, turning his life upside down.

Tommy comes to terms with the reality of his broken family as a result of a shocking experience with his father. When a freak accident occurs, Franco must make a life-changing decision, and Chief Reilly is forced to expose a family secret in order to save his career.

Tommy takes one step forward by convincing Janet to leave Roger but two steps backward when she stumbles onto his latest fling. The boys convince Sean to date a woman but neglect to tell him that she is actually a he. Franco discovers he can't shake his newfound fatherly instincts.

When Tommy asks for extra vacation time, Chief Reilly tips him off on how to get a free two week vacation from headquarters. While building a deck for Tommy's neighbor, Tommy takes advantage of his "free" advice which leads him to make a bold move in reconciling with Janet.

Tommy attempts to handle the insanity of his father while defending Colleen's new lifestyle to Janet. At the firehouse, Sean and Mike the Probie unknowingly launch a full blown wager among the crew.

When Tommy discovers a secret that Janet is keeping from him, he must come to terms with the possible consequences. At the firehouse, Chief Reilly preps the boys for their new female replacement. With the help of Franco and Sean, Tommy tracks down the man responsible for Billy's death.

When Tommy struggles to help Janet in a financial crunch, he must turn to his Uncle Teddy to help him out. The new female addition to the house fights to be accepted by the guys while they do everything they can to drive her nuts. Just as Mike is getting fed up from sleeping on the firehouse couch, he is offered a helping hand with a free place to stay... at a steep price.

While Tommy attempts to make reason of the chaos in his life, he continues to defy death while pulling dangerous stunts on the job. Lou admits his infidelity to his wife and receives an unexpected surprise. When tragedy strikes his family, Tommy must come to the rescue of his father.

When Janet needs more money to cover house repairs, Tommy turns to Uncle Teddy and his "little" friend to help him out with extra cash. When Franco's father has a stroke, Franco finds himself trying to juggle work and raising his daughter on his own. Meanwhile, a goodwill tribute to the firefighters lost in 9/11 goes awry and the firehouse is put in jeopardy.

Tommy's fate in the firehouse depends on vote by the crew. Tommy reunites with his dad. Franco and Laura's relationship grows.

Tommy asks his cousin for help in understanding the bizarre visions he's been having. The crew tries to help Laura understand the essence of male comaraderie.

Tommy has a chance at finding his kids with help from his oldest daughter. Chief Jerry asks his son for help when his wife's condition worsens.

Franco's addiction to painkillers has driven him to a support group to get help with his problem. A young boy clings to life after Tommy saves him from a fire. Jerry is introduced to his gay son's life partner.

Jerry forces the crew to attend a birthday party that his son is throwing for his boyfriend. Meanwhile, Tommy makes a move on Mariel after she tells him she might not be his half sister after all. Franco asks Laura to move in with him while Sheila tries to make Tommy jealous by showing off her new girlfriend.

Tommy starts taking Janet's antidepressants. When Sean meddles in Franco and Laura's troubled relationship he makes things worse. After a gay visitor, the crew wonders about Mike's sexuality.

Tommy's sister suddenly shows up in town when their dad is about to inherit a million dollars. Tommy and Janet decide to renew their wedding vows. Meanwhile, Mike is worried when he finds a lump.

Tommy copes with a tragedy. Jerry must decide what to do when his wife's condition worsens. Sean has a crisis of faith. Lou learns some shocking facts about Candy. And the crew responds to a multi-level building fire with people trapped inside.

Janet decides to meet with Tommy after not speaking with him for months since the sudden death of their son. Uncle Teddy refuses to allow anyone to help him get out prison. Tommy is shocked when he accidentally discovers just who his nephew has been sleeping with.

During a night out, Franco and Tommy meet two women. Tommy is finding himself bribing his daughter Colleen before she tells their mother about his indulgent treatment of her sister Katy. Jerry visits his wife Jeannie in her expensive nursing home and soon goes to Lou for financial help. Meanwhile John Sr. insists on having his 83rd birthday at a restaurant that no one else likes.

The crew faces more than accustomed when rescuing a man from his burning apartment; Sean has a request for Maggie's dad; Franco thinks his new girlfriend is hiding something from him; and Tommy realizes that his crew's future together may be in jeopardy.

Following a meeting with Janet, Tommy has yet another confrontation with Johnny; Teddy's conjugal visits with Ellie prove to be a letdown; and Franco tries to befriend his new girlfriend's mentally challenged brother. Elsewhere, Tommy keeps his vigil at Stack's bedside.

John Sr. ends up disappearing after arguing with Tommy about their living conditions. Tommy is none too thrilled with Lou's latest love interest, while Jerry's new woman might prove to be dangerous for him. Also, Sean and Maggie meet with the priest to discuss their upcoming wedding.

Tommy and Janet are brought together once again by another Gavin family tragedy. Jerry ends up not showing up for work. Mike decides it is time to look for some advice about his sexuality. Meanwhile, Maggie has a surprise for Sean.

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.

Tommy goes on another memorable date with Beth for the sake of the crew; Black Shawn proves himself in an unexpected arena; Franco realizes what he's really lost while Latrina shows she knows how to keep Lou happy; Dad gives Tommy some insight into his childhood

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.

After dealing with a particularly horrific accident on the job, Tommy questions his feelings in a dream sequence with his dead father, brother and son, and Jimmy Keefe. Meanwhile, Sean has an unwanted visitor at the hospital; and Lou has a very-much-wanted visitor to his apartment.

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.