The Advanced Irish Republican Army (AIRA) or Advanced IRA (・IRA Adobansudo Aiāruē) was a splinter group of the Provisional IRA. Led by Michael Connolly, they had acquired Stinger missiles which were originally given to the Afghan mujahideen by the CIA. Whereas the British police wanted to dismantle the group and prevent any terrorist attacks, the CIA was primarily concerned about erasing the existence of the missiles which had fallen into terrorist hands.

An Irish republican paramilitary force that believed in Irish reunification, the group sought to conduct an armed campaign against the British state. The reason as to why the Advanced IRA split from the Provisional IRA is unknown, but the offshoot was considered to be one of the most radical IRA factions. Their parent group had originally received firearms from Libyan leader Muammar Gaddafi, but after Gaddafi had refrained from shipping further weapons via a North African route, they decided to procure smuggled weapons from other sources. Connolly's wife Chloe Reddington was one such person who helped her husband secure negotiations to procure firearms from American gunrunners. During their existence, the Advanced IRA had clashed with the Metropolitan Police Service and had killed several police officers, two of them being Mabel and Sadie.

Due to the North Africa gun smuggling route being cut off, the Advanced IRA began to buy weapons from gunrunners in the United States. Accordingly, faction leader Michael Connolly ordered his second-in-command, Cillian McGrath, to go to the U.S. and complete a weapon smuggling deal. Being accompanied by other IRA members, Cillian met with gun smugglers in the Eastern U.S. to acquire weapons, particularly Stinger missiles. However, during the meeting at night, several ATF agents raided the place and ordered everyone to freeze. The criminals shot back in response, prompting the ATF agents to return fire, killing the gun runners and some IRA members. Cillian and Ian managed to escape onto a motorboat and fled by water, but Ian was fatally wounded, causing grief to the former. He returned to the United Kingdom, having successfully secured the delivery of the weapons. As a result, the Advanced IRA decided it was time to plan out a terrorist attack on a British air force base using the missiles.

However, a surviving arms dealer testified to the U.S. Congress about the history of the Stinger missiles having originally been in the hands of the Afghan mujahideen. Due to the negative image the CIA would have if the missiles' history were to be proven as fact to the public, the agency decided to help the United Kingdom's Metropolitan Police Service (MPS) track down the missiles and stop the Advanced IRA's terrorist plot. The CIA had an ulterior motive to destroy any evidence of the missiles' existence, viewing the foiling of the terrorist plot with secondary importance. At a hideout, Cillian spoke with Michael one-on-one, with the latter having been informed an American agent was coming to the isles to retrieve the Stinger. The second-in-command was visibly sad and told his boss about Ian's death, prompting Michael to offer brief condolences before telling him about the American agent. Admitting he was unsure if the American was part of the ATF, FBI or CIA, he assured his subordinate that their main obstacle was the London police.

To his chagrin, Cillian rhetorically asked how many more young men he would send to their deaths. Infuriated, Michael could not believe he would ask that and shouted that they would never stop fighting no matter how much blood was spilled until they saw the day of a united Ireland. Calming down, he claimed to Cillian he understood his sadness about Ian and added that the deaths of their brothers and sisters could not be in vain. Shouting that they would drive the Brits out of Ireland, he quieted down again and advised Cillian to go home and let his dog Quinn comfort him, so the latter left the office without saying a word. At the same time, an informant within the Advanced IRA told Eda and London police officers Jerry Smith and Emily Thompson about the group's recent weapons shipment, so the CIA agent went by herself to Gravesend to stop the cell of IRA members at a port warehouse.

In Gravesend, several of the republicans hid as she arrived and revealed themselves to order her to surrender. One of the men insulted her because she came alone and let her "Yankee arrogance" control her ego. Declaring that they would make an example out of her, the guerrilla claimed he did not care that she was a woman and would display her corpse on Tower Bridge for all to see. Immediately shooting and killing the man, Eda commented that she was tired of his sermons. Immediately, the other guerrillas began shooting at her from multiple directions, causing Eda to run away and shoot back, successfully hitting some of the guerrillas. Taking cover, one surviving fighter pulled out a grenade and attempted to throw it, but Eda shot him. To her shock, the live grenade fell near some oil drums, making Eda panic right as a huge explosion happened seconds later.

About a day later, the same informant whom Eda previously interrogated confessed that he learned about the information he had given her from Chester Shankly. He specified that Shankly frequently hanged out at the pub Whelan's in Watford, though unknown to her, the Advanced IRA was anticipating the law enforcement officers to come. Subsequently, Cillian and several IRA extremists waited outside the back of the pub in different positions to ambush them. Upon seeing Eda, Jerry and Emily enter the pub, Chester ran to the back and exited the door, and as he ran out, the extremists opened fire on the three pursuers. As Emily and Jerry managed to fend off some of the extremists, Cillian ran away from the van he used as cover and entered the pub to ambush Eda from the backdoor.

She heard the door open and turned around, instinctively charging her shoulder into his abdomen before he could fire. The two began to struggle and missed their first shots. Eda took aim at him after she pushed his arm away, but Cillian kicked her pistol out of her hand. Countering again, she grabbed his exposed foot and pushed it upward to upset his balance, punching him in the face. Cillian dodged Eda's second punch and backed away. They smirked and commended each other's endurance, but they were interrupted by Emily ordering Cillian to surrender. Refusing to do so, the second-in-command bid goodbye to the CIA agent and ran to a fence. Though Emily took aim at the extremist, Eda blocked her line of sight because she needed him alive.

Afterward, Cillian returned to one of the Advanced IRA's hideouts where Michael was finishing a call concerning their weapons shipment. Walking into the office, Cillian complained that his mission was essentially acting as a decoy to lure out the police. Ignoring the complaint, Michael said he was disappointed that Cillian could not kill the agents, especially the American among them. Apologizing for it, Cillian reasoned that she was tougher than expected, but Michael responded it did not matter since they needed to plan their next move. That night, the right-hand man felt he had nothing to lose due to losing so many comrades and decided he would die fighting the next time he encountered the police. Cillian thus handed over his dog to his neighbor Abbott, who falsely believed she was watching the pet since he was going on another "business trip." Additionally, he discreetly met up with his comrade Morton and ordered him to intentionally tip off the authorities about the Advanced IRA hideout from where they planned to launch the missiles at the air force base.

The next day, Morton bombed a car outside New Scotland Yard as Eda and her group exited the headquarters, running away before being shot in the leg. He quickly told Eda the location of the next terrorist attack while Michael and Advanced IRA subordinates were picked up by a delivery van to travel to the missile launch location, which was in a small neighborhood. Unknown to the Advanced IRA, Morton's leak allowed for the air base to halt all takeoffs and landings as well as giving the police and military time to mobilize against a potential attack. Eda also drove Jerry and Emily to the hideout located a few kilometers south of the air base. As they headed there, an elderly Advanced IRA extremist began setting up the Stinger missile while Michael advised his subordinates to exfiltrate the hideout as soon as they fired one missile. When the CIA agent and police officers arrived, Michael was told that their van was most likely a police car, making him believe that an insider must have tipped off their location to Morton since the latter was not officially informed about it.

When Jerry knocked on the front door, the Advanced IRA extremists opened heavy fire on the officers. Going to the back, Eda sneaked into the back door and turned around the staircase corner when she and Cillian saw each other. The latter shot at her, forcing her to take cover as he urged Michael to escape through the window. When Eda shot back, Cillian laid on his stomach as Michael jumped out the window and onto the ground, being spotted by the two officers as he began fleeing. Jerry adamantly ordered Emily to pursue him despite her hesitancy so that the extremist leader did not escape. Beginning to tail him, both Emily and Michael exchanged gunfire with one another, with the former yelling that she would not let him escape. Taking cover behind a tree, she exchanged more gunfire with him until he ran out of ammunition after insulting her. Before he could reload, Emily shot him once in the chest, knocking him down. Glaring at Michael, she told him that two years ago, one of his bombings killed two of her best friends from the police academy. Not regretful, Michael proclaimed that he would send her to hell and lifted his pistol. Acting fast, Emily shot him once in the head, killing him.

In the house, the exhausted Eda assessed that she could question Cillian about the Stinger knowing that he led the arms trafficking deal in the United States. While waiting for an opportunity to attack, to Eda and Cillian's shock, the elderly extremist pointed his Stinger at Eda and declared that they would not go down without using the missile that took so much work to acquire. Eda jumped to the ground as the man fired the missile, but to their surprise, the Stinger missile turned out to be a dud and merely fell down the stairs onto the ground without exploding or deploying its flight rotor. Improvising, the extremist pulled out a grenade, but Eda shot him a second later before he could throw it, instantly killing him. Running down the stairs from the live grenade, Cillian jumped over the stair railing and reloaded his rifle, dodging Eda's shot. As he turned around, his rifle barrel got stuck between two stair balusters when Eda kicked it downward, mocking him for using his large gun in such a small place. She pinned him against the wall at gunpoint and rhetorically asked if he deliberately told the Advanced IRA car bomber where he was. Eda demanded to know where he got the Stinger from, but he only answered that such a question would do her no good.

Irked, she threatened to shoot him full of bullets if he did not talk. Holding onto her pistol and pulling the barrel to his forehead, Cillian grinned and encouraged her to kill him, taunting her for not following through on her threat. He took her off guard by attempting to pull the trigger, causing her to point the pistol away as the shot missed him. Cillian grabbed her neck and tried pushing her downward, but Eda pushed her foot against him and flipped him over her using his weight. Eda frantically crawled for her pistol as Cillian tried pulling his own pistol from his coat. As they aimed at each other, they both shot at the same time, but Cillian was shot in the abdomen, admitting he underestimated Eda for intentionally missing his head. Frustrated, she yelled that she would have gladly killed him if she did not have orders to follow, ordering him to fess up.

Claiming he still had the advantage, Cillian elaborated that he had seen many of his comrades slain in the dozen or so years he had been fighting. He professed that his peers became younger as time passed, mentioning that all of their deaths haunted him. Annoyed even more, Eda retorted that she did not come to the U.K. to hear his whining. Cillian reminded her that she came to get information from him, rhetorically stating that he won if she could not get it out of him. Suddenly, he deployed a sleeve gun on his right arm and pointed the pistol under his jaw. Giving a final smirk, Cillian asserted that he and his comrades would win in the present and the future, then killing himself. With the deaths of the highest-ranking Advanced IRA members as well as the defeat and capture of other extremists, the group had effectively ceased to exist.

After the police operation which foiled the air base attack, no one outside of those involved knew about the deaths of Michael Connolly and Cillian McGrath. Although the Advanced IRA was effectively no more, their gunrunning allies in the United States, particularly the Fenians, were still at large. Chloe Reddington, Michael's wife, did not learn about her husband's murder. Exploiting this fact, the CIA had Eda pose as Chloe in order to speak with an intermediary who would give her the details about the next arms smuggling deal which was to take place in the United States.