Martin David (Willem Dafoe), a mercenary, has been tasked by a pharmaceutical company Red Leaf, to hunt and kill the last known Tasmanian Tiger. Journeying to the Australian wilderness, he stays at the house of a local woman Lucy Armstrong (Frances O'Connor), her daughter Sass, and her son nicknamed Bike. Martin, a reserved, quiet man opens up around the family even as tension in the town boils over. He discovers from Lucy that her missing husband was tasked by Red Leaf to find the Tasmanian tiger but he turned against them when he figured out their true purpose.
Jack Mindy (Sam Neill) who had watched over the Armstrong family, calls Red Leaf about concerns with Martin (having no clue Martin is a mercenary and who he is really contacting). Red Leaf hires another mercenary who burns down the Armstrong home, killing Lucy and Sass, and making Bike an orphan. Martin finds the remains of Lucy's husband, concluding he was killed by Red Leaf. The other mercenary tracks down Martin, but Martin gets the drop on him and kills him. He confronts Jack on contacting Red Leaf, saying they will do whatever it takes to "get what they want" and indirectly makes it clear his call to Red Leaf got Lucy and Sass killed, leaving an remorseful Jack to live with the guilt.
Martin continues to hunt for the Tiger, when it appears near him one day. It sees Martin and gives him a sad expression. Martin shoots and kills it, then proceeds to sob over personally causing the extinction of a beautiful creature. He then cremates the remains, deciding to not take any samples as he was directed. He calls Red Leaf, telling them what they want is gone forever, and they shouldn't bother trying looking for him. Martin tracks down Bike and Bike happily embraces him. It is implied since Bike has no family left, Martin will become his guardian having regained his humanity being around Bike and his family.