24 is a thriller that purports to be shown in "real-time," with each minute of airtime corresponding to a minute in the lives of the characters. This real-time nature is emphasized by an on-screen digital clock appearing from time to time—this corresponds roughly to the minute of the broadcast hour, factoring in commercials. The writers often take advantage of the real-time nature of the show by having the characters place time windows on certain events such as terrorist threats, thus strongly hinting that the attack/event will occur before the end of the episode.

The action switches between different locations tracing parallel adventures of different characters involved in the same overarching plot. The result is long sections of unseen narrative for each character. A main character might only be seen for a quarter of an episode's overall running time. The notice preceding each episode announcing that "events occur in real time" was only included in the first three episodes of the first season, as well as the premieres of the second and third seasons .

Over the course of the hour, three minutes are added to the clock during commercial breaks to allow time for the opening "previously on 24" segments and the preview of the next episode over the closing credits.

24 employs fast-paced and complex plots. A recurring theme of 24 has characters faced with the decision of whether or not to let something tragic happen for the sake of a greater good. In Season 2, a member of the presidential staff has the chance to warn CTU of an imminent attack on their building, but believes that doing so would put the culprits on alert and thus cause a valuable trail to go cold. A similar situation occurs prior to an attack on a shopping mall in Season 5. In Season 3, the President and CTU agents must choose between the life of a high-ranking CTU official and the imminent threat of further attacks. Season 4 is notable for a scene in which two men—one of whom possesses crucial information—lie dying in an emergency room, creating the ethical dilemma of whom to save. In addition, the sitting President often has to deal with a similar quandary. In the first hour of Season 6, Jack Bauer is asked to sacrifice himself in exchange for the location of a known terrorist.

The first season began and ended at midnight, leading to the situation that the main characters had to go almost two days without sleep. Bauer's sleep deprivation featured heavily as a plot element in the series. Later seasons have tended to use a less punishing time window, starting in the morning.

Early on, the series frequently used split-screen action to follow multiple plots, although in later seasons this was scaled back somewhat and confined mostly to phone conversations and shots leading into and out of commercial breaks.

The Counter Terrorist Unit (CTU) is a real elite branch of the United States Central Intelligence Agency (CIA) created after the 1993 World Trade Center Attack. Its headquarters are in Washington, D.C. with satellite operations in major cities where threats are likely. CTU's primary mission is to disrupt and destroy foreign and domestic terror cells hostile to the United States, as well as protect the U.S. from terror attacks. With an office in nearly every major city of the U.S., CTU also has a role in creating security policy and fighting groups of organized crime that fund terrorism.[3]

CTU offices are run by a Director, also called the Special Agent in Charge, to whom the Director of Field Operations and the Chief of Staff report. The CTU offices report to a Divisional Office, overseen by the Division Director. Divisional offices cover a larger amount of territory in their jurisdiction. Finally, the Divisional office and all other offices report to a District Headquarters, overseen by a Regional Director. This title implies that each District Headquarters has jurisdiction over an entire region of the United States.

Season 1-3 showed Jack's personal demons result from his pressures with his family and job, the coping with his wife's death, his reconnection with his daughter Kim, and the sacrifices he makes to eliminate threats to his country.

In Season 1, Jack was seen trying to hold his family together with a threat looming over them. At the end of the Season, Teri has been killed. In Season 2, Jack is a wreck resulting from his loss, and Kim has become distanced from him as a result. In Season 3, Jack and Kim have gotten back on track, but in his last operation, Jack has become addicted to heroin, reason being to keep his cover with drug dealers, but evidently to himself, and to one or two others, it was to cope with Teri's death.

Another connecting narrative were the consequences of a failed assasination mission in which Jack was in command of years before Season 1 took place. The main antagonists behind Season 1 were the Drazen Family, whose head of the family, Victor Drazen, was the target of that mission. The main antagonist of Season 2 was Peter Kingsley, an American big oil mogul who organized a conspiracy to allow the Second Wave terrorist cell to detonate a nuclear bomb to make his oil holdings skyrocket in the event of a war. The main antagonist behind Season 3 was Stephen Saunders, a British Intelligence Agent who was a part of the team on the Drazen Mission, thought to be dead. Being left behind on that mission was the source of his hatred to the USA, which led to the terrorist events in Season 3.

In the finale of Season 3, the stories of many of the main characters were resolved; Kim and Chase, her current boyfriend, decided to leave CTU, David Palmer vouched not to run for re-election, Tony is sent to prison for treason, leaving Michelle with an incarcerated husband (she would later leave him), and Jack is fired from CTU (which is seen in the prequel to Season 4). In addition to Teri Bauer, other key characters were killed off throughout the first 3 seasons, including George Mason, Ryan Chappelle, Nina Myers, and Sherry Palmer.

Beginning with season 4, a new storyline for 24 began, as the only remaining regular character was Jack Bauer in the beginning. As a result, there was little continuity from the past 3 seasons until the later returns of Michelle Dessler, Tony Almeida, and David Palmer.

The events of Season 4-6 were the foreground of two narratives, intertwined with each other. One was Jack's opposition towards the Chinese, as a result of a raid on the Chinese Consulate in Los Angeles. The other was a conspiracy, in which was part conceived by Jack's very own father and brother.

To follow a lead to stop the antagonists of Season 4, Jack and his team broke into the Consulate to extract a man with infomation. A fire fight ensued in which the Chinese Consulate was killed in the cross fire. As a result, the Chinese launch an investigation and discover Jack was in command of the operation. As a result, they demand that the US President, Charles Logan, hand Bauer over to them. Fearing that Jack would reveal vital intel to the Chinese, he arranges Jack to be killed by the secret service agent sent to pick him up. Jack is informed of the attempt on his life, and to escape, fakes his death and flees to Mexico, only known to be alive to four people.

In Season 5, David Palmer, Michelle Desler, and Tony Almeida (three of the four people who knew Jack was alive) are killed, leaving Chloe O'Brien to be the only one remaining that knew Jack was alive. Jack returns to LA to find the culprits, and is found to be still alive and aids CTU in stopping the latest threat from Eastern European extremists. Doing so, he finds out that Charles Logan was behind the threat with another man, at the time only known as Graem. Their intention was in the end to allow the US to expand their military presence in Central Asia, but the terrorists found out, and changed their plans to attack the US. Once Logan was caught, the Chinese find Jack, take him prisoner to China.

When Jack is exchanged at the beginning of Season 6, his role becomes much more prominent, helping to stop Islamic Fundamentalists detonate nuclear devices in LA. In the process of the Day, Jack finds out that his brother Graem, seen in Season 5, and even Jack's father were involved in the conspiracy with Logan, and that the nuclear weapons being used on US soil were supplied by their family company. Once the threat is eliminated, Jack learns that the Chinese are holding Audrey Raines hostage, Jack's love interest since some time before Day 4 and daughter to his former boss, ex-Secretary of Defense, James Heller, and want something from Jack. Jack initially was told she was killed in a car accident while looking for him in China, however, the Chinese kidnapped her in order to use her as leverage against Jack. Jack was ordered by Cheng Zhi to retrieve a device in the nuclear bombs he just captured and give them to Cheng Zhi in exchange for Audrey. The prototype would give the Chinese access to all of Russia's defense technology. First, Jack tricks two military guards guarding the bombs into letting him go take it, but Mike Doyle was quick and stopped Jack and placed him under arrest. President Palmer then issues Jack's request, only for it to be rejected by Vice President Daniels after Palmer falls unconscious once again. Mike Doyle and Jack Bauer team up to go to Cheng Zhi and give the prototype to him, but the trip is cut short when Doyle receives a call from Buchanan telling him to take Jack back to CTU and into custody. Jack hears this and points his gun at him, telling him to pull over so that he can drive to Cheng Zhi alone. CTU gets wind of this, and now Jack Bauer has become a rogue agent.