Tom Smith is an agent with MI6.
At least he was an agent, back in the 70s when the story begins. Okay, it truly starts in 1968 but it will be the 70s the mystery that plays the key role in these adventures begins. And in 1968 he was working for that department's sister agency, MI5. But he will shortly afterwards make the switch over to external security from internal and it will be while now working for MI6 that the mystery takes place.
The mystery being, "What happened to Tom Smith?"
We are given a brief recount of Smith's life leading up to his employment with MI5 and then MI6. He had been serving in the Royal Air Force for a while back in the late 50s when he meets and marries Pat and in 1964 leaves the military to take a job as a carpenter. IN 1965 their son Jack is born and life is pretty good for the three of them.
A bit thereafter is when a talent scout of sorts from MI5 who had had his eye on Smith for some time makes his pitch to get Smith to join the organization. Smith was seen as a very bright young man who was spending some of his free time teaching self-defense classes to local kids. A sharp individual with an ability to take care of himself was the sort of person MI5 could use.
So the offer is made and then accepted and Smith spends the next couple of years in that employ. Then he is scouted and recruited by rival MI6 and an offer is made and then accepted and now Smith is in MI6. The travel is wider and often for a bit longer but the family, to Smith, is forever something to come home to. And he usually does. Until he doesn't.
And that is the mystery that his son Jack, now quite a bit older, decides at long last to investigate. What happened to Tom Smith, nicknamed Hong Kong Tom when he was stationed in that British colony at the time he vanished. The last time he was officially heard from was when the penthouse apartment of the sitting Governor of Hong Kong exploded. After that, nothing.
That is what the majority of the adventures we will be allowed to read deal with: what was the kind of work he did in the Far East and what was he doing during the 70s, 80s, and 90s.