Giustozzi, together with a group of anonymous colleagues, spent two years interviewing members of jihadist groups active in Khorasan, a region that includes parts of Afghanistan, Pakistan, and Central Asia. The book provides extraordinary depth and detail, yet Giustozzi still manages to show the forest along with the trees. As its home base in Iraq and Syria collapses, the Islamic State (or ISIS) is looking for a new home. Khorasan offers big advantages over Libya, Yemen, or the Sahel: it is close to China, Iran, and Russia, and to U.S. forces based in Afghanistan. The ISIS affiliate known as the Islamic State in Khorasan receives around $300 million each year from outside donors, mostly individuals from Kuwait, Qatar, and Saudi Arabia, but the governments of those countries contribute, too. The ISK wants to absorb the Taliban and then take the fight to its external enemies, above all Iran. The ISK's greatest hope is Iran’s fear: that the Taliban will cut a deal with the Afghan government that will discredit the group among true believers, sending recruits to the ISK.