Hopetown, South Africa, the 1870s. Englishman Stafford Parker is trying to persuade Boer leader Jan Bloem to hand over control of a potential diamond field, to the disgust of Bloem's nephew Piet Quieman and businessman Muller, who has got rich through selling cheap rum to black workers.

Parker meets new arrivals: father-and-daughter missionary team the Harts, and David Raymond. Parker's friend Brandy Bill informs him that a diamond has been found on Bloem's territory. Parker rides to see Bloem and successfully persuades him that he alone can maintain law and order and regulate the processing of the diamonds. Piet joins them to try to get a deal for Muller, but Bloem berates him for telling lies.

Parker and the Hopetown inhabitants, including bar-keepers Ma and Dora Bracken, set off in a wagon train, where they establish a new settlement at Klipdrift. Muller attempts some rabble-rousing, but Parker decisively wins the resulting fight.

Six months later, Klipdrift is a thriving town. Elderly former jeweller Pinto wants to join the prospectors, as he never earned enough to buy his wife a diamond. When Brandy Bill discovers a ten-carat stone, Parker offers it to Pinto to cut. David is suspicious that Muller is buying diamonds directly from the natives, side-stepping Parker's arrangement with Bloem, but he has no evidence.

At Klipdrift's first anniversary party, Parker announces that 1,856 diamonds have been registered at his office. Dora and the other girls put on a song-and-dance show. A prospector named Rogers drunkenly spills the beans to Parker about Muller's activities, unaware that Muller is listening.

Next day, Parker goes to see Muller and demands to know why he hasn't registered a ten-carat diamond. Muller denies all knowledge, and says that Rogers cannot confirm this as he fell over a tentrope the previous night and broke his neck.

At a town meeting, Parker calls for a rulebook to be drawn up, and all the diggers to sign it. Pillories are erected in the town centre. Mary is shocked to see them, and unconvinced by Parker's explanation that they're a substitute for an unaffordable prison. They go for a walk and swap life stories, including Parker's confession that he left the navy under a cloud and has been his own man ever since.

The first diggers' court meets, and tries a native accused of stealing diamonds to sell. He is ordered to name the purchaser, but he singles out Timothy Maxie rather than Muller. An angry mob torches Maxie's property and flings him into the river. While attention is distracted elsewhere, Muller shoots the pilloried man dead.

A jealous Dora warns Mary to keep away from Parker, though is eventually persuaded (after a fight) that Mary is the one he truly wants. However, when Parker proposes to Mary, she is hesitant.

Piet and Muller meet Bloem, who is unhappy about what he hears but reluctant to break his deal with Parker. Muller changes his mind after persuading him that there may be war.

In Klipdrift, Parker announces that the town is too big for the current arrangements to continue. He proposes an official constitution. Bloem, Muller and Piet ride into town, but their attempts at withdrawing Parker's concession are rebuffed. Muller threatens war.

Mary and David are becoming noticeably closer, to the point where the latter is thinking of leaving. But when Mary tries to tell Parker about this and her concerns about widespread gambling and drinking, he angrily refuses to let her impose her prejudices on others.

The inhabitants of Klipdrift prepare for conflict. The first Diggers' Republic is proclaimed, and its flag raised. Muller's men camp outside, and Parker, on hearing that they plan to attack at dawn, stages a pre-emptive strike. David is shot during the resulting conflict, but Muller is soundly defeated and paraded through Klipdrift in humiliation.

Parker visits the casualties, and sees that David and Mary have become inseparable. Queen Victoria's representative Longdon arrives and tells Parker that the diamond fields have been annexed by Britain. Parker announces that he plans to seek gold in some nearby mountains - and tells a crestfallen Dora that he'll be going on his own.