Frederick Forsyth's The Afgan
Sometime before the events of the story take place, a joint MI6/CIA/ISI raid against al Qaeda (AQ) operatives in Pakistan uncovers documents concerning a planned, but largely cryptic, terrorist attack. This raises concerns and triggers further investigations authorised at the most senior level.
Mike Martin, is now a retired SAS officer. Educated in Iraq and physically able to pass for an Afghan (his maternal grandmother was a Bengali-Indian named Indira Bohse who contributed to his chestnut-brown complexion which somehow makes him look like an Arab (or later on, Afghan) Martin has a near-perfect command of Arabic and is also familiar with Afghanistan and the Pashtun language, Pashto. He is chosen (due entirely to an overheard gaffe by his brother who is a member of the expert "Koran committee" of academics specialising in ancient texts) to infiltrate the highest echelons of AQ, by impersonating an AQ prisoner, Izmat Khan, currently held at Guantanamo Bay. In the story it is revealed that prior to Martin's escapades in Iraq he had worked with the Mujahideen in Afghanistan during the Soviet occupation where he met Osama Bin Laden and rescued a young Afghan boy, Izmat Khan, who later became a resistance leader. Khan is portrayed as an heroic Afghan freedom fighter determined to have vengeance against America and careless of his life following the bombing of his village in the Tora Bora mountains which killed his family.
In a highly covert operation Martin is successful in impersonating "The Afghan" (under the code word "crowbar"), a prisoner held in Guantanamo Bay for over five years. Following his re-infiltration to Afghanistan as a repatriated prisoner, and his subsequent stage-managed escape, he makes his way back to an al Qaeda safe house in Pakistan, where he is accepted as a compatriot following his security clearance by "The Sheik", Osama Bin Laden due to the brief encounter years before.
He makes contact with AQ and volunteers to get involved in a suicidal terrorist attack which involves hijacking and re-berthing a tanker off Borneo carrying liquid petroleum gas. Another group hijack a cargo ship in the Caribbean, although this is intended to serve as a cynical decoy. Martin successfully alerts his handlers to the general nature of the threat, but is left incommunicado for several weeks as the ship steams to the US Eastern Seaboard. Despite general mayhem and murder, Martin does not appear to have an actual job description in the plot and never gets personally involved in murdering or torturing any innocent bystanders, so is effectively a supernumerary.
Izmat Khan escapes from US captivity after a US fighter jet accidentally crashes into the secret hiding place in Washington state where Izmat is incarcerated, destroying his guards and the compound wall whilst leaving him unscathed and free to walk out. He is finally shot dead trying to warn his allies using a public phone in Canada, after a long chase across the Cascades.
Eventually the tanker reaches the mid-Atlantic, where a G8 summit is, imaginatively, being held on the Queen Mary 2 liner. Martin finally learns that the terrorists intend to release and then ignite the gas on board the tanker, which could incinerate the Queen Mary 2 as it passed within range. Martin's last minute heroism, quick reflexes and self-sacrifice prevent a tragedy.
10/10 in my opinion, I couldn't put it down once I started reading it. Well worth a read