Far from the battlefields of Iraq and Afghanistan, the US and al-Qaeda are fighting a clandestine war of drones and suicide bombers. It began in 2006, when twenty-three men escaped from a political prison in Yemen's capital. Later they were joined by a dozen men released from Guantanamo Bay. Now, they stand ready to hijack the Arab Spring. Unrivalled Yemen expert Gregory Johnsen takes a look at the threat, and introduces his new book, The Last Refuge – the first account of al-Qaeda’s explosive growth in the country.