HBO has built its reputation on stellar TV dramas like The Wire and Game of Thrones, but both shows owe a debt to Tom Fontana’s gritty prison drama, Oz; it was the one that started it all.

Like The Wire, Oz engaged with social issues around race, masculinity and the fatally flawed justice system; and like Game of Thrones, Oz was unpredictable. Characters came and went with wild abandon, often quickly going from key players in the ensuing drama to just another body on the mortuary slab. Danger lurked at every turn, and viewers learned not to get too attached to any of the complex characters on display. The worst imaginable thing could and quite often did happen.

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Oz was brilliant, but it wasn’t perfect. The show’s cancellation after six seasons and 56 episodes left plenty of questions unanswered.

Yuri Kosygin is still in the hole

Yuri Kosygin arrives during Oz’s third season with a reputation as one of the Russian mob’s most ruthless assassins. However, he soon meets his match when attempting to take out compatriot Nikolai Stanislofsky in the prison library, on the orders of Ryan O’Reilly. While both men survive, Kosygin is sent to the hole and then solitary confinement before seemingly disappearing altogether. Though a deleted scene exists in which Kosygin is "taken out" by a mysterious woman called Lana Keese, who claims to be visiting him from the State Department, that explanation was cut from the episode, leaving his fate unknown.

William Giles' whereabouts

William Giles was an Oz mainstay for much of Season 2 through 5. Neither insane nor mentally deficient, Giles remained a strange enigma, splitting his time between one-word riddles and acts of unspeakable violence. The debate around his mental state and whether he was fit to stand trial or even do time was a key plot point, particularly when Giles’ violent actions saw him facing the chair. Yet despite making his struggles an important part of Oz for much of the show’s run, fans were never given any closure over his fate, with Giles disappearing after the fifth season.

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The Aging Pill

Arguably Oz’s most contentious storyline centered on the introduction of experimental “aging pills” which were offered to inmates with long sentences so they could be released early as old men. Created as a means to ease overcrowding, the experiment seemed to be going fine at first but then the test subjects began dropping like flies. Cyril O’Reilly’s developed an alarming grey streak of hair and, though the experiment stopped, grim repercussions appeared likely for all involved. Only, there weren’t. Sensing, perhaps, the outlandish nature of what they were proposing, the storyline was dropped, never to be spoken of again.

The Mafia's man on the inside

For much of Oz’s first two seasons, the prison’s Italian-American contingent benefited from the outside assistance of investigator Lenny Burrano. Evidently on the Mafia payroll, Burrano worked closely with Nino Schibetta, his son Peter, Antonio Nappa and Chucky Pancamo, passing back news and orders from “the family” while maintaining his role among the staff on the prison. An intriguing character and plot ultimately reach a dead end, however, when Burrano disappears. This follows a botched attempt at taking out Simon Adebisi that ends in grim and humiliating fashion for Peter Schibetta and Pancamo. Quite where Burrano went or why is never explained.

Frank Urbano dodging death row

Over the course of Oz, any prisoner offing another inmate usually ended up in the chair. Yet Urbano is the exception and it is never explained why. An enforcer for the Italians and Chucky Pancamo during the show’s fifth season, it’s Urbano who deals the fatal blow to the show’s narrator-of-sorts Augustus Hill in the shocking season finale. However, when the sixth season begins minus Augustus, Urbano remains in Emerald City as happy as anything, having escaped any additional consequences. Quite how or why Urbano is able to evade the kind of punishment dished out to Cyril O’Reilly is unclear.

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Jonathan Coushaine's GED classes

Though Oz regularly stretched the limits of believability, there were generous doses of reality along the way — like the Season 2 storyline that saw some inmates go back to school to get their GED. Comedian Bryan Callen, who is best known for The Goldbergs, appears as Jonathan Coushaine, a former high school teacher turned inmate who is tasked by McManus with teaching his fellow reprobates. It’s a great storyline and one grounded in painful reality, yet by the time Season 3 rolls around both Coushaine and the GED storyline as a whole are gone.

Alonzo Torquemada's motivations

While Season 6 of Oz was the last to be broadcast, it wasn’t necessarily intended to be the final one. Creator Tom Fontana always kept the door open for a potential return, meaning some plotlines were left open or, in the case of Alonzo Torquemada, never quite came to fruition. Played by Bobby Cannavale in a brilliant but often forgotten performance, Torquemada arrives with just two episodes remaining, intent getting everyone hooked on his "product" and “becoming” Miguel Alvarez, his new obsession. Though Torquemada’s on his way to both by the end, much about his character and storyline still remains unresolved.

Poet's telemarketing credit card scam

Oz’s final episode wrapped up plenty of long-running storylines, some conclusively, others less so. But one character largely absent from the focus of the feature-length finale is Poet. One of the few inmates to survive the entirety of the show’s run, by the end he’s working for the in-prison telemarketing firm, having given up his other nefarious activities. However, unbeknownst to his foreman Burr Redding, Poet has hit upon a scam with the other Homeboys involving customer credit card numbers. An intriguing development, but one that is never ultimately resolved, with the telemarketing continuing on uninterrupted into the show’s finale.

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The fallout from the toxic fumes leak

In another deadly twist during the already eventful sixth season of Oz, toxic fumes begin leaking from the air ducts in Emerald City’s solitary confinement wing, resulting in one casualty and several seriously ill inmates. The consequences are pretty severe given that inmate Carlos Martinez has lost his life (unbeknownst to them, not from the poison), while the wise-cracking loner Greg Penders is suing the state for endangering his life. Penders even tries to get Martinez’s family and fellow victim Omar White in on the legal action but the storyline soon fades into oblivion along with the prison’s alarming toxic leak concerns.

Tobias Beecher’s uncertain future

Another storyline left hanging in the balance come the big Oz finale. Beecher may have offed Schillinger and seen Keller go flying over some prison railings to his own dark fate, but his own future is far from clear. He could be heading for life imprisonment, he might be heading for the chair. He may even end up getting away with it all, scot-free. Though the show strives for an air of ambiguity when it comes to Beecher, who is arguably the closest thing Oz has to a protagonist, it ends up feeling more like unfinished business come the show's end.

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