It is 1999 and the troubled West African nation of Sierra Leone is ravaged by major political unrest. Rebel factions such as the Revolutionary United Front frequently terrorize the open countryside, intimidating Mende locals and enslaving many to harvest diamonds, which fund their increasingly successful war effort. One such unfortunate is fisherman Solomon Vandy (Djimon Hounsou), from Shenge, who has been assigned to a workforce overseen by a ruthless warlord, Captain Poison (David Harewood).
On a particularly tense morning, Vandy discovers an enormous pink diamond in the riverbank and buries it in the soft earth. Captain Poison learns of the stone, but before he can act on this knowledge the area is raided by government security forces. Both men are subsequently incarcerated in Freetown along with Danny Archer (Leonardo DiCaprio), a white Rhodesian gunrunner jailed while attempting to smuggle diamonds into Liberia for corrupt South African mining executive Rudolph van de Kaap (Marius Weyers).
Having managed to learn of the pink diamond’s existence, Archer arranges to have Vandy freed from detention. He then travels to Cape Town, meeting with his former military contacts, including Colonel Coetzee (Arnold Vosloo) – an Afrikaner late of the apartheid-era South African Defence Force now freelancing with a private military firm. Archer remarks that he hopes to abscond with Vandy’s stone and leave the Dark Continent forever, but Coetzee indicates that his lost stake in Archer’s botched Liberian operation entitles him to the diamond as compensation. The former returns to Sierra Leone, locates Vandy, and offers to help him find his family if he will recover his prize.
Meanwhile, RUF insurgents initiate an escalation of hostilities. Freetown falls to their advance while Vandy’s son Dia (Kagiso Kuypers) is among those rounded up to serve as a child soldier under a liberated Captain Poison. Archer and Vandy narrowly escape to Guinea, where they plan to infiltrate Kono with an American journalist, Maddy Bowen (Jennifer Connelly), in exchange for giving her inside information on the illicit diamond trade. Coetzee and his private army also turn up in the region, having been contracted by local authorities to repulse the renewed rebel offensive.
While Bowen is evacuated with her story, the two men set out for Captain Poison’s former encampment on their own. Dia, now stationed with the RUF garrison there, is confronted – although he refuses to acknowledge his father. Archer radios the site’s coordinates to Coetzee, who directs an air strike via an Mi-24 helicopter gunship. Vandy locates Captain Poison and beats him to death with a shovel while attacking mercenaries rout the warlord’s surviving men. Coeztee then forces a reluctant Vandy to produce the diamond, but is shot by Archer, who has deduced that he will have them both eliminated once their usefulness has expired. Dia holds them both at gunpoint, although Vandy convinces him of his own retained innocence and the two consummate their previous bond.
Archer discloses he has been mortally wounded and cannot proceed as anticipated. He entrusts the stone to Vandy, ordering him to take it for his family. Vandy and his son rendezvous with a charter pilot, Nabil (Jimi Mistry), who flies them to safety while Archer makes a final phone call to Maddy Bowen, charging her to assist Vandy, as well as giving her consent to publish his revelations of the diamond trade, telling her “It’s a real story now”. Gazing across the landscape, he grasps a handful of bloodstained earth and dies peacefully, fulfilling Coetzee’s prediction that the smuggler would never leave his African home.
Shortly afterwards, Vandy, who is now living in England, meets with representatives of van de Kaap, who wishes to acquire his jewel. Bowen photographs the deal for publication in her article detailing the trade in conflict gems and exposes van de Kaap’s criminal actions. Meanwhile, Vandy’s guest appearance at a conference on “blood diamonds” in Kimberley is met with a standing ovation.