Smokescreen by Dick Francis

Edward Lincoln is a action movie film star, but his family life is quiet, a lovely wife (Charlie) and three children, two sons and a daughter with retarded development due to brain injury.  Nerissa is his substitiute mother, she asks Edward to go to South Africa to find out why her horses are no longer winning and he swiftly becomes embroiled in a thriller to more than equal his films, including three attempts on his life (electrocution, burial in explosion at gold mine and abadonment in car in Kruger National Park), a brilliant calculating killer, entrapment attempts by a beautiful girl and the highest stakes: a gold mine, prizewinning horses and Edward's own life.