Trackers is based on a novel written by Deon Meyer.
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Here is the goodreads synopsis of Trackers:
Lemmer's First Law: Don't get involved. But when Emma le Roux looks at him with pleading eyes, when the roof of his Karoo house needs big repairs, when the cause is good and just, laws can be broken. So he sighs, and says, yes, he'll ride shotgun for two rare black rhinos. Bad decision. Because on a dark and dusty road in Limpopo, they stick a Smith & Wesson Model 500 against his head. They kick him and beat him, they lie, they deceive him, and they steal his Glock, the one with his fingerprints all over it. They should have killed him. And now he goes after them--the start of a trail of violence that will run the length and breadth of a country, and touch many lives.
It will leave a trail of blood through the first private-investigation dossier of former cop Mat Joubert. It's a "fifty-five," police slang for a missing persons case. It will stomp fear and horror through the life of Milla Strachan, who walked out on her rich, cheating husband and abusive teenage son to start a new life. A trail of death, stretching from the Chizarira to the Cape Waterfront. And at the end of it, nobody will be untouched.
Source material: cinemax.com