Buck Riley Jr, also known as Book II, is the son of Buck Riley Sr, and occasionally works under Shane Schofield in the U.S. Marines.
After he turned 18, Buck Riley Jr followed in his father's footsteps and joined the United States Marine Corps. He often heard his father talk about his commander, Shane Schofield, about how good a leader he was and how the other Marine was like a son to him, though how Buck Jr took this is uncertain.
While Buck Jr was in training, Book died on a mission in Antarctica, and the circumstances were never divulged to him or his mother. When Buck Jr's mother was forcibly moved off of the base as a result, she committed suicide soon after; to her son's grief, it was because of her inability to live without Buck Jr's father.
At some point in the two years after his father's death, Buck Jr was given the call-sign Book II in honour of his father, and eventually assigned to the Marine Helicopter Squadron 1, under Schofield's command. Knowing that Schofield had led his father on the mission in Antarctica, Book II wondered if Schofield might have been in some way responsible for his father's death, and so rarely spoke to him and tried to get a measure of his character.
After they arrived at Area 7, Book II joined his fellow Marines in one of the offices while the President was toured around the facility. He listened as the other Marines discussed what Area 7 was for, and spoke up when Elvis suggested it was for building a superbomb. Book II pointed out how several conspiracies were just that, and asked if Schofield had heard of any of the ones he had listed, to which Schofield evenly admitted that he'd heard of the last; a plane that could actually turn invisible.
Soon, the Marines and Presidential staff witnessed a base-wide broadcast from a rogue Air Force Colonel known as Caesar, announcing his intention of a coup d'etat against the President. As the 7th Squadron forces opened fire on the Marines, only Book II and Elvis managed to escape the office before it was hit by a rocket. The pair managed to use a cockroach to cover their escape to the personnel elevator, and were joined by Love Machine and Calvin before they entered the elevator and climbed on top. After the shaft began filling with water, the group was forced to emerge onto Level 5, where they raided a weapons cabinet before meeting up with the President and his remaining security detail by the prisoner cells. Book II and the others came under fire when the emerged onto Level 4, and Book II's inadvertent shining of his flashlight in an attacker's eyes saved him.
After Schofield and his group forced the Alpha unit to retreat, Book II listened in as the President and Herbert Franklin explained Area 7's purpose to produce a vaccine for the Chinese bio-weapon called the Sinovirus. He then joined Schofield, the President and Janson as they donned the gear of fallen Alpha unit men and bluffed their way among the Bravo unit team guarding the Football. Once the President had reset the Football's timer, Book II helped cover him back to the aircraft elevator.
As the group prepared to leave Area 7, they found that a South African scientist and the Reccondos had taken a genetically-engineered boy critical to the Sinovirus vaccine and fled to Lake Powell. Book II prepared the X-rail to transport them out, only for an assault from Bravo unit to force most of their team off the X-rail before it departed. Schofield ordered Book II to continue their pursuit of Botha, though when the young Marine questioned retrieving Kevin over protecting the President and by extension the country, Schofield informed him he'd never lost a countdown, and that the President would be fine under Gant and Mother's protection.
When they arrived at Lake Powell, Book II piloted his shared bipod with Schofield as they chased after the Reccondos, only for the arrival of 7th Squadron's Charlie unit to make things harder. The pair took control of a Super Stallion after they lost Brainiac and Franklin, using it to track Botha. When they came face to face with a Penetrator, Book II was shocked when Schofield ordered the other chopper to draw before shooting down the missile and the Penetrator, and Book II criticised Schofield's risky strategy. When they located Botha, their Stallion was shot down by the other Penetrators, and they were only saved from death by utilising Botha's plan for themselves by using air from an underwater gas station and a tunnel leading to a hideout.
When they used a Tiger Moth to start making their way back to Area 7, Schofield asked Book II why he didn't like him. The young Marine demanded to know how exactly his father had died, learning that Buck Sr had been hung over a pool of killer whales after being captured saving a young girl. Book II told Schofield of the circumstances of his mother's suicide, reminding the Captain that risky strategies have consequences, but since his father had not died as a direct result of Schofield's plans, informed him that he was still making up his mind on what he thought of him.
When they returned to Area 7, Book II was separated from Schofield as he attempted to get the Football to the President, and was able to avoid getting captured by the loose prisoners. He made his way up to the main hanger where he saved Janson from Boa. The pair took off after Seth Grimshaw and Goliath, who had taken the Football and were attempting to escape from the base. Book II found himself forced to fight Goliath, who used his own gun to shoot the young Marine in the bicep. Before he could be strangled, Book II used the magnetic head of his Maghook to attach itself to a steel plate in the prisoner's skull, and while Goliath flailed about, Book II fired the Maghook and was sent flying backwards as Goliath's skull cracked.
With the Football secure, the injured Book II and Janson took refuge in a control tower until Schofield returned with the President and Kevin. Book II showed Schofield how Area 7 was set to self destruct soon if they didn't stop it, and to make matters worse, Caesar sent out a new broadcast, revealing that, like the President, he had a transmitter on his heart, and by dying in the destruction would cause the plasma warheads around the country to detonate. Because of his injury, Book II had to remain behind to guard the President until Marine reinforcements arrived, while Schofield went to try and stop Caesar.
Once the Marine forces arrived, Book II and the others relocated to Area 8 until the crisis was over.
A couple of weeks later, Book II and the others were awarded classified Congressional Medals of Honour for their actions in saving the President's life.
Sixteen months later, Book II was part of Schofield's team as part of a mission to an abandoned Soviet missile silo, which turns out to be a trap in order to kill Schofield. Book II is the only other survivor of the incident, and after reuniting with Mother they are rescued by the Black Knight, and Schofield sends Book II and Mother to London to find a Mossad agent with information.
However they are attacked by a bounty hunting team called IG-88, and while their target is killed, they manage to collect a tape with information. After the President tells Book II he has access to all of the U.S.'s resources to keep Schofield alive, Book II watches the tape and learn that M-12, the twelve richest men in the world and the ones behind the bounty, plan to start a new Cold War.
Book II heads to New York to create an uplink for Schofield so that he can disarm the CincLock-VII security system M-12 is using to launch the Chameleon missiles, and his team defeats the enemy forces there. He later appears at Mother's barbeque, explaining his version of events to her and David Fairfax.
Book II was reassigned in the Corps to another unit while Schofield and Mother moved on to other duties.
A very quiet individual, Book II can sometimes be mistaken for being rude until it is realised that he just doesn't like talking unnecessarily. Unlike Schofield, he prefers to take caution before acting rather than outright risk everything, knowing that there are consequences to such strategies. While he was at first wary of Schofield's methods, he eventually comes to trust him and his judgement.