Smokescreen by Dick Francis

This is the one about the movie actor. It is also largely set in South Africa. The title is, I think, a rather strained play on the fact that the hero/detective is a screen actor and the fact that much of the action is orchestrated by the bad to hide what he is up to.

Horse racing is definitely a side issue although it does occupy a large share of pages. A friend of action movie hero Edward Lincoln has inherited a string of race horses in South Africa from her sister. Without explanation, the horses have all started to perform poorly and she asks Link to just run out to Jo'burg and see what is going on - and to please do it before her own death from cancer.

In South Africa, Link finds himself suddenly accident-prone, and no mere dropping teacups. A microphone electrocutes the woman who has just taken it out of his hand. A bump on the head down in a gold mine leaves him stranded in the dark as the day's blasting is about to take place. The final attempt on his life abandons the appearance of accident and resets the scenario of his latest film, which closes the plot loop neatly.

Even so, Link breaks the "depressed hero" pattern pretty well. We do learn that his youngest child suffered traumatic brain damage in an accident as an infant. Still, his family seems happy and satisfied with their life away from the glitter of wherever the British version of Hollywood is located - and Link, himself, is more than happy to get home to them when he can.