Day of rebellion - Johnny O'Brien

When Jack Christie's father disappears, the time-travelling teenager and his best friend Angus track him to a strange ice-bound future where China has evolved into a global superpower. Time has splintered and Jack and Angus must discover the Point of Divergence - the moment that history altered.
Travelling back to 1860, they find themselves in the midst of the bloody Taiping Rebellion: a world of China warlords, empires and brave rebels. But Jack and Angus possess an object that all the warring factions want and, it's not long before the boys find themselves - and the future of the world - in grave danger.