Breslin served as the narrator of Narcos: Mexico, and is the first fictional protagonist of the Narcos series.
It is unknown when Breslin joined the DEA, but by the mid-1980s was stationed in Houston, Texas. One night in 1984, his fellow agent Sal Orozco told him to come to a strip mall in the city, where he found his brother Greg murdered inside his car with an eight-ball of cocaine by side.
His brother's death had a significant impact on Breslin's life. He felt that he needed to protected his widowed sister-in-law Alejandra and her son Danny. He also vowed to do his part in putting a stop to illegal drug trafficking into the United States of America.
After the Guadalajara cartel kidnapped, tortured and murdered DEA agent Enrique Camarena Salazar in February 1985, Edward Heath appointed Breslin as the head of Operation Leyenda, the clandestine DEA operation to bring the perpetrators of Camarena's murder to justice and bring apart the destruction of the Guadalajara cartel.
As a part of the operation, he entered Mexican as a tourist and met up with Special Agent Kenny Moss and presented them with a chargesheet containing names of the individuals they needed to arrest.
Breslin, who previously made several contacts with Mexican police officers hire Ossie Mejía, Amat Palacios and Danilo Garza as mercenaries. The CIA supplied them with one of the several tapes of Camarena's interrogation, and they began going after the men whose voices were recorded, and eventually identify the doctor as Delgado, who was a practicing pediatrician in Mexico City.
In January 1986, the team abduct Delgado in broad daylight, and threaten him in giving up the name of Camarena's interrogator, active CISEN agent Sergio Espino Verdin. After securing permission from Heath, Breslin and his team ambush Verdin's convoy, kill his escorts and kidnap him.
Verdin, like several other DFS agents was trained in torture by the CIA during Mexico's Dirty War in the 1970s, and hence was resilient against the DEA's attempts to extract information from him. Breslin also pointed several flaws in the modus operandi of the DEA team, pointing out that they were only a few miles from his scene of abduction, left a witness alive, did not take shortcuts and did not board up the windows, and warned them to let him go before his fellow agents discover him. Verdin remained quiet, despite Breslin slicing several fingers off his hands. Verdin also taunted the Mexican mercenaries, prompting Ossie to shoot him in the gut out of frustration. Breslin seized the oppurtunity, and promised medical assistance to Verdin if he revealed the names of Miguel Ángel Félix Gallardo's political contacts. Verdin gave out the name of Rubén Zuno Arce, who owned the mansion where Camarena was tortured, and the team dumped his body outside a hospital, but Verdin succumbed to his injuries.
Félix Gallardo is informed of the kidnapping of two men associated with Camarena's murder by Juan José Esparragoza Moreno, and he warned Zuno to stay safe in the city. However, Zuno fled to the countryside, and became paranoid thanks to his cocaine abuse. Disregarding orders of the military sergeant protecting him, he fled his safehouse and entered a plane destined to another town in the countryside, but unbeknownst to him, Breslin had bribed the American pilots of the plane, and the plane landed in Texas, where Zuno was arrested by the American police, and was handed over to the DEA.
Upon interrogation by the DEA, Zuno revealed the principal source of Félix Gallardo's political protection, his uncle and Mexico's Secretary of Defense Andrés. Meanwhile, while in the United States, he met Alejandra and took Danny fishing.
However before the grand jury in which Zuno would be tried took place,Félix Gallardo made a deal with the CIA in which he would smuggle weapons from America to Nicaragua, in exchange for the CIA pulling strings and preventing the DEA operation from damaging his organization. As a result, Zuno said during his trial that he never met Félix Gallardo before. Breslin stormed out of the courtroom, and vents his frustration by throwing a trashcan into a mirror.
After the trial ended, he attended a meeting which included Heath and DEA Administrator Jack Lawn. The meeting is interrupted by Ted Kaye of the State Department, who instructed the DEA to end Operation Leyenda after the capture of Zuno. Breslin angrily lashed out at Kaye, resulting in Kaye belittling Breslin and the DEA. After the meeting, he placed an envelope full of cash at Alejandra's doorstep, and went to a diner, and confronted Guillermo Calderoni, who had been following Breslin for a while.
Calderoni, who was despised by the DEA for allowing Félix Gallardo to escape in 1985, offers to work with Breslin to bring down the Guadalajara cartel. Breslin was reluctant to trust Calderoni, but the Mexican police commander said that his position with in Félix Gallardo's organization would be useful for the Americans, since he was reluctantly forced to work with Félix Gallardo after he gained support from the Minister of Defense.
Back in Mexico, Breslin introduced Calderoni to his team. Calderoni provided significant chunks of intel to the team, informing them of a spat between the Tijuana and Sinaloa plazas, and that Amado Carrillo Fuentes would be visiting Belize that year to buy several jet planes from a bankrupt airline. Acting on his intelligence, a part of team followed Sinaloan smugglers Cochiloco and Chapo move a truckload of their cocaine, which they stored in one of Benjamín Arellano Félix's warehouses. They believed that the truck was heading towards the United States, but follow it actually headed into a warehouse into the city. The team break into the warehouse, and discover an entrance to an underground tunnel. Rather than calling the Mexican federal police, the DEA agents leak the information to the Arellano Félix brothers, which resulted in Ramón Arellano Félix storming the warehouse, and dropping explosives into the tunnel, and killing several survivors..
Meanwhile, Walt followed Amado to Belize, and attended the auction which Amado attended. After Amado purchased six Boeing 727s, the team sneak into the airfield at night and install trackers on the planes. They return to Mexico, and track the jets to an airfield in Chihuahua. The team decide to not share the information with Heath and the Mexican police.
Later, Heath informed Breslin about a female informant having intel on the Guadalajara cartel, and ordered him to travel to Ojinaga to meet her. He found the woman to be Mimi Webb Miller, whose boyfriend was Pablo Acosta, the leader of the Juarez plaza of the Guadalajara cartel. Mimi's man forced a bag over Walt's head and they took him to Acosta's hideout in the cab of a pick-up truck. There, Acosta asked Walt his reason for joining the DEA to which Walt shared the story of the death of his brother three years ago. Acosta explained to Walt that Mimi insisted on him leaving the drug business, which he began contemplating after he felt that he didn't fit in after moving to the cocaine business. Walt then gave the number of the motel he was staying in, and Mimi dropped him back at his motel, and told him that she was pregnant with Acosta's child.
Before the team could move on the planes, Acosta gave an interview to an American newspaper, and revealed the working of the Guadalajara cartel, and promised more interviews. The interview put him in the crosshair of the American and Mexican governments, who were both intertwined in the cartel's corruption. Walt then went to visit Mimi's house, but found the house to empty. He is then knocked out cold by two FBI agents, and when he woke up, they tell him to stay away from Acosta as they've received orders from higher ups to take out Acosta. They proceed to mock the DEA, calling them one step up from Park Ranger.
At the behest of Mimi, Walt drove to Pablo Acosta's stronghold of Santa Elena in Chihuahua, hoping to convince the drug lord to enter witness protection in the United States. However, Mexican police officers launch an aerial raid from the American side of the border, assisted by the FBI, and began indiscriminately firing at civilians and gunmen alike.
Acosta locks himself up in a house, which is surrounded by the FBI and the MFJP. Calderoni arrived at the scene, and told Walt that he couldn't allow Walt to escort Acosta to America, since Acosta's death was already decided by the higher-ups, and also that if he killed Acosta, he could improve his standing within Felix Gallardo. Walter disregards the FBI, and walked into the house, and convinced to get Acosta across the Rio Negro by acting as a human shield, since he, as an American federal agent, could not be shot by the MFJP and the FBI. Walt also told Acosta that he spoke to Terrence Poppa, and knew that Acosta would not give anymore interviews since he hated the idea of being a snitch, and told him to escape to America for the sake of his unborn child. Walt manages to get Acosta a few meters outside the house, but Acosta steals Walt's gun and lunges at the police, and was shot to death in front of Walt.
Afterwards, the team decide to raid the cartel's airfield in Chiapias and burn several kilos of cocaine hoping that it would prompt retaliation from the Colombians and end the Félix's empire. The team commander three cartel trucks, and race to the airfield, and began lining up the packs of cocaine to set it on fire. Danilo Garza notices that the cocaine is heavier than usual, and finds out that it is some other power after tasting it. Immediately, he is shot by a sniper, and cartel gunmen turn on the floodlights. The team realize that it was an ambush, and took defensive positions and returned fire, but end up losing all of their Mexican mercenaries. Walt, Sal and Amat made a run for the woods in order to escape, but Amat is shot and lay wounded just outside the bushes where Walt was hiding. He is immediatelly surrounded by two cartel gunmen, but at that moment, Calderoni arrived. As Walt watched from the bushes, Calderoni executed the two gunmen, but more gunmen began to swarm to the scene, forcing Calderoni to shoot Amat in the head, instantly killing him; despite Amat agreeing to pretend that they don't know each other. Walt reunited with Sal in the safehouse, and they told Daryl that they've lost everyone.
After the airfield disaster, Walt is summoned to the DEA headquarters, and a senior official chided him for continuing on with Leyenda despite the operation officially ending after Zuno's arrest. Walt is transferred to a desk job in Tulsa, and is told by the officer the DEA would not fulfill the wishes of the dead Mexican mercenaries, since they were criminals and they didn't owe anything to the DEA. He is ordered to work a desk job in Sacramento.
Later,he is informed of a cocaine bust in a warehouse in Sylmar. Knowing that the DEA didn't investigate the location, he concluded that cocaine confiscated was the same cocaine which Félix delivered from the Chiapias airbase.
In April, Calderoni invited Walt to Guadalajara to witness the arrest of Félix Gallardo. Breslin went to the house Félix was hiding, walking past Félix as he sat at the back of a police vehicle, locking eyes. Walt told Calderoni that he still wouldn't consider him a friend, to which Calderoni replied that he needed friends in his line of work. After the arrest of Gallardo, Breslin is congratulated for the successful completion of Leyenda by Kaye and the State Department. Breslin discovered that Kaye had completely forgotten about their earlier meeting, and tells Heath that the certificate is worthless. He is then transferred to El Paso, working under bureau leader James Kuykendall.
Breslin went back to Laredo, and using the influence of his boss Kuykendall, he got permission to visit Félix Gallardo in prison. Félix Gallardo refused to reveal the extent of his political power, and mocked Camarena's torture. When asked about the future of Mexico, Félix accurately predicted the future of Mexico leading to the Mexican Drug War. He informed Walt about war breaking between the Sinaloa and Tijuana cartel, and the massive power accumulated by the Juarez and Gulf cartels. He also told Walt to remember the name of Carrillo Fuentes, who according to him, would become the most powerful drug trafficker Mexico could ever see.
|"The Plaza System"|
|"Rafa, Rafa, Rafa!"|
|"The Colombian Connection"|
|"La Última Frontera"|
|"Jefe de Jefes"|
|"Just Say No"|
|"811 Lope de Vega"|
|"Salva El Tigre"|
|"Alea Iacta Est"|
|"Ruben Zuno Arce"|
|"The Big Dig"|
|"Truth and Reconciliation"|
|"Se Cayó El Sistema"|
|"Growth, Prosperity, and Liberation"|