The successors "to the strongest"

The king is dead, long live his successor! The young King of the Kaldonians, Alastair, lies dying in an Asian palace, surrounded by his generals and subjects. Alastair has conquered a vast empire but has no children and his natural successors are considered unsuitable heirs by his generals.  The foot soldiers, however, retain loyalty to the royal family and force the commanders to accept Alastair's obscure half-brother and unborn son to be made joint monarchs. Many of the generals see opportunities for themselves to carve up the empire but are suspicious of each other of wanting to usurp the puppet kings and seize total power. What is behind the spate of unnatural deaths spreading from the palace, through the city, that draws an ordinary brother and sister into an alliance with two exotic adventurers to stop a world-threatening menace? Looking on are the conquered people of the empire. Is this the time to throw off the yoke of Kaldonian oppression for the restoration of their ancient liberties? As predicted by the dying Alastair, only the strongest would be his final successor.