Ryan's happy when his mom, Suzanne Fitsgerald comes to Oz to start an inmate arts education program.He's so excited, he forces inmates to sign up for the program. Still not trusting of Jia Kenmin, he's further riled when Li, a new asian inmate, arrives and gets close with Jia. After these two threaten to harm Ryan's mom, Ryan approaches Li and stabs him. The plan backfires when Cyril picks up the shank and finishes the job killing Li. This gets Cyril thrown in solitary and sent to trial for murder. When Cyril's conviction is handed down, Ryan attempts to get his family to gather funds for an appeal. This attempt fails miserably as his family rejects this option. Ryan next delivers on a pact with Morales - he'll kill Jia Kenmin in exchange for Morales "injuring" Shupe - the inmate Ryan doesn't want to rat on him. In true Ryan O'Reily form, Ryan sets up a fight in the gym with Jia so the hacks can see it. While in the infirmary, he lies to one of the guards about Jia calling the guards wimps. This angers the guard so he and two other guards visit Jia in his cell and deliver a fatal beating. During Cyril's trial, Father Meehan - a local priest- arrives as Ryan's new podmate. Ryan's history with the church and Priests fuels the anger and resentment he shows towards Father Meehan. The tension builds even more when Meehan offers to assist with Cyril's defense but Ryan refuses. Meehan finally confronts Ryan about his anger and Ryan breaks down telling Meehan how his father was responsible for killing his baby sister. The guilt Ryan carries is from him thinking he actually could have prevented it.
Season 4 Part 2
Ryan is intrigued at the prospect of a television crew coming to Oz to film. He devises a plan to get an interview with the crew only he recognizes the television reporter as one who did a scathing story on Ryan and Cyril when they were in the Irish gangs. For revenge, Ryan gets Cyril placed in a pod with the reporter and then, gets Cyril into a frenzy. Cyril, angry and out of control, beats the reporter to a pulp. The consequences of this are high as Ryan discovers McManus' plan to transfer Cyril to the psychiatric hospital because he's not responding to drug therapy. Ryan immediately goes to Dr. Nathan to get help to escape... which she refuses to do. Next, he gets visited by his birth mother. Although he doesn't believe her at first, he gets confirmation in from his father. Through more visits, Ryan learns that his mother's a fugitive who's preparing to turn herself in. Although Ryan protests this decision, she explains that life is better lived truthfully than on the run from a lie. Meanwhile, Ryan has taken up with new inmate Connolly -- an Irish terrorist with plans to blow up Em City. Just as Connolly prepares to detonate the bomb, Ryan has a change of heart and warns McManus only in his haste to tell McManus, he leaves the gas stove on. The inmates are ordered out of Em City to avoid harm from the possible explosion. Connolly's bomb doesn't go off but a guard's lit cigarette ignites the gas Ryan left on in the kitchen and Em City explodes.
Season 4 Part 1
After he discovers new inmate Gulino's cell phone, Ryan sets out to get it. Stanislofsky tricks Gulino into giving him the phone so Ryan must figure out how to get the phone for himself. He decides to tell Hoyt to shank Stainslofsky by telling Hoyt that Stanislofsky implicated him in Gulino's murder. During a confrontation between Hoyt and Stanislofsky, the phone gets dropped and Ryan immediately picks it up. But Ryan's happiness is short lived because the phone gets discovered during an inspection. While Ryan plans revenge, new inmate Keenan arrives and immediately announces his desire to get in O'Reily's good graces. To show his poweress, Keenan proudly describes the details of his rape of Dr. Nathan. This brings Ryan to the boiling point and he immediately kills Keenan by smashing his skull with a barbell. On the family front, Ryan decides to seek help for Cyril's nightmares but Sister Pete tells him that they both must participate in the victim offender program with Dr. Nathan and her in-laws. Ryan reluctantly goes only he again vehemently professes his obsessive love for Gloria.
Ryan's plot to get Schillinger shanked by Hoyt fails. Ryan returns to selling tits, something he promptly stops after being threatened by El Cid. Ryan then turns his attention to training his brother Cyril for the Oz boxing tournament. To give Cyril an edge, Ryan spikes Cyril's opponents' water with Chloryl Hydrate and then, he starts betting on these bouts and makes a killing. But his fortune comes to an end once Officer Murphy discovers Ryan's secret. Murphy tells Ryan that Cyril will fight on his own or O'Reilly goes to, and stays in, the hole. Knowing that Cyril's opponent, Khan, will pulverize his brother, he gets their father (whom Ryan and Cyril both hate) to visit. This visit enrages Cyril and, sure enough, Cyril takes his anger out in the ring, delivering a brutal beating that puts Khan in a coma.
Hoping to get a piece of the drug trade, Ryan rats to Schibetta that Adebisi killed his father -- conveniently omitting his part in the deed. Dr. Nathan finds a cancerous tumor in Ryan's breast. He bellows his disbelief to her, but eventually submits to further testing and surgery to remove the tumor. While recuperating, Ryan falls passionately in love with Dr. Nathan, whom he calls his "guardian angel." He soon begins obsessing over her with love letters and calls -- he even divorces his wife, telling her he's found someone else. Deciding that he's the only man for Dr. Nathan and no one else should have her, he tells his slow-witted brother Cyril to kill her husband. Cyril does the deed but ends up joining Ryan in OZ as an inmate. Ryan now must protect his brother. Finding out that Schillinger raped Cyril, he swears revenge.
Ryan uses his connections with the CO's to get transferred to Em City. Once he arrives, Ryan immediately goes to Nino Schibetta (runs the drug trade in Oz) and offers his loyalty. After Dino Ortolani is killed on orders from Jefferson Keane, Ryan arranges for Keane's elimination by having the CO's stage a confrontation between Keane and two Latino inmates. Keane kills one of them and is sentenced to death. This works perfectly for Ryan and Schibetta moves him up the drug trade ladder in return. Ryan soon partners with Adebisi to eliminate Schibetta so the two of them can control the business. Unfortunately Ryan starts using drugs with Beecher as his "get high" partner. When the riot breaks out, Ryan joins with Said and the others to negotiate with the officers.