Mandela left Ethiopia safely, but had only returned to South Africa incognito for a few months, when he was detained. He would stay behind bars for 27 years.
US diplomat and CIA spy Donald Rickard revealed just prior to his death in 2016, that the CIA had tracked Mandela's movements and passed them on to the Apartheid regime which arrested him. He said they did so because they feared he would facilitate the spread of communist ideology across Africa.
And that is that.