Back Blast is an action thriller novel by Mark Greaney, published on February 16, 2016, by Berkley Books. It is the fifth book in the Gray Man series, featuring assassin and former CIA operative Court Gentry. The novel follows Gentry as he seeks answers for the shoot-on-sight sanction by his former CIA employers against him.

After five years overseas as the Gray Man, Court Gentry goes to Washington, D.C. to seek answers for the shoot-on-sight sanction imposed by the CIA's director of clandestine services Denny Carmichael against him. He robs a meth stash house owned by the Aryan Brotherhood to steal cash and a weapon, which attracts Carmichael's attention as well as Washington Post investigative reporters Andy Shoal and Catherine King.

Carmichael and his deputy Jordan Mayes bring in programs officer Suzanne Brewer and Gentry's former team leader Zack Hightower to a task force dedicated to hunting down Gentry. They also task a Joint Special Operations Command (JSOC) unit instead of the CIA's Special Activities Division (SAD) due to Carmichael's rivalry with its head and Gentry's former boss Matthew Hanley. In addition, Carmichael secretly reaches out to Saudi intelligence's D.C. station chief Murquin "Kaz" al-Kazaz for help with capturing Gentry.

Meanwhile, Townsend Government Services head Leland Babbitt threatens Carmichael with leaking classified information to the United States Congress after Carmichael distances himself from Townsend House following their recent failed attempt to capture Gentry in Europe. Carmichael brings in Babbitt to the task force, but orders him killed. Gentry watches Babbitt in his house when he is assassinated by Hightower with a sniper rifle. He evades Babbitt's security force but is wounded by Saudi assassins disguised as D.C. police before escaping.

The next night, Gentry visits Hanley at his house. Hanley tells him that Carmichael, the CIA director, and then-chief counsel Max Ohlhauser signed off on the shoot-on-sight because Gentry had killed a non-combatant in his last CIA operation codenamed Back Blast, where he extracted a Mossad deep-penetration agent codenamed Hawthorn in Trieste, Italy who was compromised by Al Qaeda, killing an AQ assassin sent to eliminate him. After thwarting a robbery at a convenience store, Gentry tracks down Ohlhauser, who repeats Hanley's answer while also revealing that the Autonomous Asset Program (AAP), a classified training program Gentry was part of before joining the SAD, is still operational. Gentry is identified through facial recognition by JSOC operatives, allowing Kaz's men to capture him at a Washington Metro station at Dupont Circle. Suspicious of his captors, Gentry fights them off and escapes while Ohlhauser is killed in the crossfire.

A Crime Stoppers tip leads to Gentry's hideout being raided by D.C. police, forcing him to set up camp in an abandoned Civil War-era grain mill outside the capital. He also reads an article written by King about a domestic terrorist targeting CIA personnel, unaware that Carmichael is using her as bait. Gentry tracks down the reporter and discovers Hightower following her. Gentry abducts his former team leader, who tells him about the hunt and admits his involvement in Babbitt's death. They part ways, as Hightower later relays Gentry's concerns about the Saudi proxy force to Hanley.

Gentry next reaches out to King and asks her to confirm details about Operation Back Blast with Mossad officer Yanis Alvey, who had helped him get to the United States but was briefly placed under house arrest afterwards. He also learns that Carmichael told her about his birthplace in Jacksonville, Florida, which he interprets as a threat. He goes to Glen St. Mary, Florida to find his estranged father James, who is interrogated by CIA officers about his son's whereabouts. He sees Gentry and warns him to stay away. After finding out that his father's interrogators are AAP trainees, Gentry decides to infiltrate their training grounds at Harvey Point in North Carolina.

Meanwhile, Shoal finds evidence of the Saudi proxy force being involved in Ohlhauser's death, which is intercepted by Mayes. He confronts Carmichael, who admits to his secret pact with Kaz as Shoal is later assassinated by the Saudis. Fearful for his life, Mayes meets with Brewer and tells her about the Saudis as well as Operation Back Blast, intending to inform the Justice Department. They are attacked by the Saudi assassins. Brewer crashes her car, killing Mayes, and blackmails Carmichael into calling off Kaz's men.