There was a children’s TV programme broadcast by the BBC in the late 1960’s / early 1970’s.
It was an mystery / adventure type and featured a teenage boy, a girl (I think) and a man trying to solve the mystery of a box? If my memory serves me correctly it was an overseas’ series that had been dubbed. I’m afraid I don’t remember much else, except enjoying it.
For the life of me, I can’t remember the programme’s name.