The Freewheelers are an unofficial group affiliated with MI-6.
The genesis of the group, one which usually consisted of three teenagers, two male and one female, came about when the first three to become the team found themselves involuntarily mixed up with trouble by a former Nazi named Von Gelb who wants very much to undo the terrible calamity (his opinion) that was the downfall of the Third Reich.
The three young people, Bill Cowan, Gregory Phillips, and Mary Maude, were having considerable trouble staying alive against Von Gelb and his rather extensive enterprise when they got unexpected but much needed help by Colonel Buchan (or Buchanan, I've seen it both ways but the former is most prevalent). The Colonel was an experience agent with MI-6 and well aware of the danger posed by Von Gelb. He was also smart enough to know that those these young adults were not trained operatives with years of experience, they were undoubtedly resourceful and, due to their predicament, already deep in it.
So, without planning but also with considerable incentive, the group which would come to be called the Freewheelers came into being. The idea of using non-professionals for particular missions was not new to MI-6 or Buchan but to employ such young people was and with the new alliance would come a lot of learning problems for both the trio and their unofficial leader.
The make-up of the Freewheelers would change occasionally as eventually each member would move on with his or her life. Cowan would hang around for some time while Phillips would be replaced with Nick Carter and soon after Maude would make room for Olga Yevchenko. That young woman would soon step aside for Fiona and so on.
Mike Hobbs and Sue Craig and Steve Walker would show up after a bit and stay for a good time but even they would move on. Even their boss, the Colonel, would leave, getting a promotion placing Major Colin Wade in his stead.
No matter the make-up, or the adult leadership, the Freewheelers would prove over and again that they were a very valuable, and entertaining, part of the British Secret Service.