Early in 1944, a Special Operations mission was parachuted into Serbia to make contact with a group of Bulgarian partisans operating in the area. The mission, of which Frank Thompson was a member, was under the command of Major Mostyn Davies; its remit was to arrange air-drops for the partisans to assist their operations against the occupying Royal Bulgarian Army, and later in the extension of guerilla warfare across the frontier into Bulgaria itself. When Mostyn Davies was killed in action, Thompson assumed command of the mission and crossed the frontier with the partisan brigade in mid-May. By the end of May, the whole group including the British mission had been killed or captured. After a show trial held in the village of Litakovo, Frank, although a British officer in uniform, was executed by firing squad together with the remaining leaders of the partisans and villagers who had aided them.