On 30 November, 1803, a corvette sets sail from the port of La Coruña amidst cheers and applause. It holds twenty-two orphaned children whose mission consists of bringing the recently discovered smallpox vaccination to the overseas territories. They are accompanied by Isabel Zendal, who is there to take care of them. The heroes of this hare-brained expedition, which is led by the doctor Francisco Xavier Balmis and his assistant Josep Salvany, will have to face down storms and shipwrecks, the opposition of the clergy, the corruption of officials and the greed of those seeking to profit at the expense of the most vulnerable.
If this adventure eventually became the greatest humanitarian feat in History, it was down not just to the courage of the children entrusted with saving the lives of so many people, but also the determination of the two leaders, fearless men fighting for the love of the only woman on board.