My wife is trying to identify a TV serial for Children (Young Teens) that was broadcast during a holiday period in the mornings sometime between 1977 & 1980. She believes it was BBC. This is all she can remember:
It started with a boy (aged about 12) visiting his mother who was recuperating from an operation in hospital. As he leaves the hospital and is walking down a hospital corridor he happens to turn and look through an open door, and sees two men apparently smothering or somehow killing an elderly lady in a hospital bed - on seeing the boy one of the men tries to shut the door. She thinks this scene was repeated at the start of each episode as it has stuck firmly in her memory.
As the boys mother is in hospital, and it is holiday time, he goes to stay with some friends who live in an old house in the country. Here her memory starts to fade - but she thinks what happens is strange things start to happen and it becomes quite scary with the boy being unsure of whom he can trust. Eventually even the people he is staying with are shown to be somehow linked with the big 'plot' that is going on.
She remembers it being scary, and the boy finding he is involved in some major international crime, of which the women in the hospital is somehow connected.
She has a vague memory of the final episode involving a last minute desperate chase to stop a concert hall/theatre being blown up - but she may be getting this last bit muddled up with something else
It sounds like your wife might be a bit muddled on some of the detail but I think the show you have referred to here is Touch and Go which was broadcast on BBC over 5 episodes from 20/09/1978 to 18/10/1978. This is the plot:
Teenage Emily has to spend the night in hospital following a minor road accident whilst on holiday by the coast. During the night she gets up and accidentally stumbles into a room where she sees a dead woman with a man leaning over her body.
The following day she is discharged from hopsital to resume her holiday. Back at her hotel she meets a boy called Charles and they soon discover they are being watched from all sides.
The plot seems to revolve around smuggling at first but soon becomes more serious when our heroes discover a plot, by a right wing group, to blow up a visiting African delegation. Naturally, the kids can't convince the authorities so decide to solve the caper on their own. They are captured but escape and then there's the frantic race against time to stop a bomb going off at a nearby Naval College.
The series was based on a 1976 novel by Josephine Poole.
I'm pretty certain this is the correct series because most of the elements seem to fit.