On December the 14th last year the BBC's Mike Thomson awoke to a desperate voicemail message. It came from a frightened mother of three in besieged East Aleppo. Head teacher, Om Modar, who had been in regular contact with Mike, was pleading for help. Syrian government forces were closing in on the rebel-held area and bombs were falling around the shelter she shared with dozens of petrified children. Her voice, crackling with fear, said: "Please, please help us get out of Aleppo by safe corridor.....we are terrified.....please help us." That was the last Mike heard from Om. Months of silence followed. Finally, he became convinced she was dead. Then out of the blue came a two-line text. It revealed the fate of Om Modar and led Mike to near the Syrian border.