In 1530 AD, Meztli and Cualli are saved from an Inca sacrificial site where virgins are left to die to appease their gods because conquistadors invaded their lands. Zolin, Meztli's childhood friend has been sent by Hermit Tupac to rescue them, which he does. They must now follow a perilous journey along Inca trails through the mountains and the safety of free Inca towns.


Etalpalli, one of the priests who brought the virgins to the sacrificial site attempts to find the pair. Conquistador Capitán Buena Giraldo teams up with Etalpalli who lies about his knowledge of a local gold mine is.


Meztli and her friends are met by Urco from Cualli's village. He has been sent by Tupac to tell them that there is no safe haven through the mountains. Instead they must use to a secret cave that goes under the mountains to a hidden valley and golden pyramid.


A far greater threat catches up with them. It is smallpox, a plague brought by the conquistadors that is devastating the local population. Only a few adults survive. For some unknown reason the conquistadors are immune and Inca children also have a high survival rate.


After travelling through the cave, Meztli and her friends arrive in the secret valley of Ehuraythak and golden pyramid to find that the entire population of adults have died from the plague and only children have survived. These are led by two twelve-year-olds, Palia and Ekko who soon welcome the four adults and the tiny community becomes self-sufficient.


Meanwhile, Tupac learns that a new order of fanatical priests have arrived to replace the original ones in the local temple who died with the plague. Their solution is to sacrifice all the children and the few remaining mothers at the next full moon. Tupac is too old to be able to stop this latest sacrifice himself so sets out to find Zolin and the maidens to ask them to return to the sacrificial site and rescue the latest victims.


On the way he is attacked by rogue priests including Etalpalli. His llama is killed and he is shot by a musket that the conquistadors have brought to their land but manages to fight them off by using his slingshot. His one thought now is to get to the pyramid but with a musket ball in his shoulder he is weak and knows that if the ball is not removed he will die.


Back at Ehuraythak, Palia and Ekko find Tupac. Though weak he survives and tells the four that they must return to the sacrificial site to rescue the mothers and children before the next full moon due to rise in only two weeks.


Meztli and her friends begin a new journey back in a race against time through hostile territory controlled by the conquistadors and rogue priests. Their success depends on the help of others and sometimes the enemy become almost friends. The cost though, is gold and a lost gold mine that Capitán Giraldo believes is still in the area.