it is a story that has not been told before, not in its entirety, told by the people who have made the journey into the mind and heart of isis. we begin with an extraordinary chance to look into the islamic state. not a single reporter has dared to venture there. since the gruesome beheadings of journalists began last year. imagine seeing this. >> i'm john cantlie, the british citizen abandoned by my own government. >> and this. >> these could be my last hours in this world. >> and then heading straight into the heart of darkness. ♪ but that is precisely what this man did. >> during the months i was preparing the trip, every night i felt a knife on my throat. i felt it. physically.