As the dark realities of apartheid-era South Africa come to light, Shack Twala (Sidney Poitier), a black revolutionary with a past spent on Robben Island, experiences an unexpected release from imprisonment, thanks to the efforts of his Afrikaner defense attorney, Rina van Niekerk (Prunella Gee). This sudden freedom is triggered by retrospective legislation that threatens to render Shack a victim again. To celebrate Rina's pivotal decision, the trio, which also includes Jim Keogh (Michael Caine), a British mining engineer who witnessed Shack's trial, pays a visit to Rina’s home. However, their joyful moment is violently interrupted by police conducting random identity checks and arrests. Disoriented from his recent imprisonment, Shack finds himself in conflict with the authorities, ultimately resulting in his handcuffing. Despite Rina’s attempts to defend him, she suffers brutal violence from a policeman, which spurs Jim into action, leaving the officer incapacitated and turning them all into fugitives.
Meanwhile, back at the police station, a police brigadier faces a fierce reprimand from the racist Major Horn (Nicol Williamson), the head of the Bureau of State Security (BOSS), due to Shack's release and the police's clumsy handling of identity checks, which ignites outrage globally.
Now hunted by BOSS, the trio embarks on a perilous journey toward Botswana with the help of Indian dentists Anil Mukarjee and Persis Ray (Persis Khambatta). Their getaway hinges on a stash of stolen uncut diamonds meant to support the Black Congress Party and its mysterious leader, Wilby Xaba (Joe De Graft). As Shack teams up with his allies, they discover the hidden diamonds at the bottom of a daunting 230-foot deep sinkhole. Under Shack’s direction and Mukarjee’s expertise, Jim successfully retrieves the precious gems. However, a critical twist arises when Persis, intent on using the diamonds for her escape, tragically murders Mukarjee and attempts to claim the fortune for herself. In a desperate struggle, Shack ultimately protects the diamonds by sending Ray to her demise in the sinkhole.
With the diamonds secured, the trio arranges for Blane (Rutger Hauer), a private pilot harboring his own secrets, to facilitate their escape. Rina skillfully manipulates knowledge of Blane's illicit activities and unapproved relationships into a blackmail scheme that ensures their safe passage.
As they approach the South Africa-Botswana border, they are caught off guard by a police ambush. Just as their pursuers close in, they narrowly escape by boarding Blane’s aircraft, only to face a fierce confrontation with the South African Air Force during their flight. After a gripping aerial confrontation, they manage an emergency landing on a makeshift airstrip. Following feeble farewells to Blane as he ascends into the sky once more, Shack and his companions head to one of the Black Congress Party's camps, where they are met by enthusiastic villagers and armed guards. However, their moment of respite is cut short when a convoy of BOSS agents launches an attack, overpowering the guards and abducting Wilby — the true target of the operation — all while unveiling the shocking truth that the diamonds were clever forgeries.
In the ensuing chaos, Shack leads the villagers to rescue Wilby, as the BOSS agents flee in a helicopter. Their assault leads to the chopper’s destruction and the downfall of its occupants, except for Major Horn, who boasts about his government's imminent rescue and his relentless pursuit of them. Unfazed, Jim responds with ruthlessness; smiling coldly, he seizes Horn’s moment of complacency to wrest away his pistol, dispatching the operative with a precise shot from his own weapon, concluding their harrowing ordeal in a dramatic twist of fate.
