Across Africa 97% of black rhinos have been killed for their horns. In 1997 the species was declared officially extinct in Zambia. But now, thanks to an ambitious reintroduction plan, they’re back. Poaching hasn’t gone away – their horns are still prized in Asian medicine. But a small, dedicated team are fighting to keep them safe. This is the frontline of conservation – it doesn’t get any tougher.