Following the shooting of series protagonist Tony Soprano by his uncle Corrado "Junior" Soprano in the previous episode, the plot of "Join the Club" centers on the now-comatose Tony, his family, friends, and business associates as they adjust to the possibility of Tony not coming out of his coma in various ways. Tony's wife Carmela, his son A.J., daughter Meadow, sisters Janice and Barbara, and nephew Christopher Moltisanti all handle the situation differently, with Christopher (also a member of Tony's mob crew) providing unlikely support for the broken-down Carmela. Tony's mafia associates, now without a leader, experiences a similar predicament as several of his subordinates begin vying for power, with Vito Spatafore showing particular interest in Tony's position. While comatose, Tony has a dream in which he envisions himself as a mild-mannered travelling salesman, not involved with the Mafia.
"Join the Club" premiered on HBO on March 19, 2006 and was generally well-received by critics and fans. Edie Falco's performance in the episode was particularly praised by critics as one of her finest of the series. Many fans were initially confounded by the unusually realistic dream sequence; it has since become the subject of much analysis.
Tony is in critical condition, two days after being shot by Uncle Junior. The attending physicians in the ICU sedate Tony into an induced coma after he awakes and rips out his breathing tube. Several doctors comment on the complications of Tony's gunshot wound, the most dangerous of which is severe sepsis, and they encourage Carmela and others to talk to him and play him music he enjoys in the hopes of a recovery. However, they also warn his family members of the "obviously negative outcome," as well as the prospects of brain damage. Carmela asks the doctor if Tony is "aware that he's dying." A vigil of Tony's family members and business associates have assembled in the ICU. A distraught Carmela, Christopher Moltisanti, and Meadow sleep in the hospital.
Uncle Junior is being held in custody and is questioned about the shooting. He is confused about the situation, hostile towards his interrogator and does not remember that he has a new lawyer. He denies that he shot his nephew and insists that if Tony was shot it must have been self-inflicted, because he is "a depression case."
Christopher, Paulie Walnuts, and Vito Spatafore vie for small opportunities to assist Tony's family during the crisis, such as sending presents to Tony's room and bickering over giving a ride home to A.J.
During the funeral wake of the late soldier Eugene Pontecorvo, an impromptu meeting of associates is held, and Silvio Dante assumes Tony's responsibilities as acting Boss. The meeting also reveals that, while most of the group is loyal to the incapacitated Tony, some are unsympathetically furious at Junior, and others are suspicious of why Bobby -— traditionally Junior's de facto caretaker -— was not in the house that night. Vito makes a bid to take over Eugene's sportsbook responsibilities, and later, suggests to Janice that perhaps Eugene had been a self-loathing homosexual who had no one to talk to.
Meanwhile, A.J. acts curiously aloof, avoiding Tony's room, and shirking his familial and school responsibilities. To the chagrin of Carmela, he talks to a reporter at the hospital, but later curses the ones camped outside the Soprano home; he forgets to bring requested items to the hospital to assist in Tony's recovery. A questionable stomach flu (which may have been faked or psychosomatic) excuses him from a night shift at the hospital and he is flippantly preoccupied with cars. A.J.'s unforthcoming behavior to his father's condition worries Carmela, who voices her concerns to Rosalie Aprile. With the death of her own wayward son Jackie Aprile, Jr., Rosalie advises Carmela to engage in stricter parenting with A.J.. In addition to the normal worries for her son, however, Carmela fears that A.J.'s deep esteem for his father is the source of his aloofness.
A.J. admits to Meadow that he is embarrassed and angry by the actions of his family, especially Uncle Junior, whom he calls a "mummy." A.J. finally concedes to his family's wishes to talk to his comatose father. Once the two are alone (and after talking about cars), A.J. vows to avenge what he believes to be his father's imminent death by putting a bullet in Uncle Junior's "mummy head." Immediately afterwards, he admits to Carmela that he dropped out of junior college.
While he is in a coma, Tony has a long dream-like experience that is woven throughout the episode. The experience begins with Tony awaking in a hotel room at a Radisson Hotel in Costa Mesa, California. He is a precision optics salesman on a business trip, without his trademark New Jersey accent. The next morning he goes to a convention and is asked for ID to gain admittance. But Tony has someone else's wallet and briefcase, a man named Kevin Finnerty from Kingman, Arizona, to whom he bears a resemblance. Tony says that he must have unintentionally picked up these items the previous evening at the hotel bar. He returns to the bar, where a group of business travelers overhear him telling his story to the bartender (the bartender joking, "Around here, it's dead"). The group invite Tony to join them for dinner, during which he discusses his 'life' in more detail, alluding to a midlife crisis by saying, "I mean, who am I? Where am I going?" After dinner, outside the hotel, Tony makes a pass at a woman from the group. She responds at first but then cuts him off. She tells him she saw his face when he got off the phone with his wife (whose voice is not Carmela's). Suddenly, a helicopter spotlight shines on the pair, to which the woman says "They must be looking for a perp". It is here that Tony awakens from his original coma, and rips out his breathing tube. He is moaning "Who am I? Where am I going?" (The latter phrase perhaps being both a reference to his life in both the dream and waking life, and his afterlife). The dream resumes when he is placed in another coma, as he checks into a different hotel under Finnerty's name. Two Buddhist monks overhear him checking in and, thinking he is Finnerty, accost him saying they had a horrible winter at the monastery because of Finnerty's heating system. Tony tells them that he's not Finnerty, which makes the monks angry; they scuffle briefly and the monks flee. The next morning, the hotel elevator is out of order, so Tony takes the stairs. As he is walking down the stairs, he slips and falls. Later, in the emergency room (in the dream), the doctor tells Tony that aside from having a minor concussion, his CT scan shows some dark spots on his brain, which indicate lack of oxygen. The doctor states that this indicates early stages of Alzheimer's disease. When the doctor leaves him at his bed, Tony is seen saying "I'm lost" to himself. After he returns to his hotel room, Tony picks up the phone, but hangs up before dialing.