In 1960, 10-year-old protagonist Arthur is living with his grandmother in a quiet country house. His grandfather Archibald has recently gone missing and he sees little of his parents. His grandmother entertains him by reading stories to him of his grandfather's adventures in Africa. One of these stories is about the friendship of the tall, Maasai-like tribe called the Bogo Matassalai with the Minimoys — tooth-sized, elfin beings they believe to be their counterparts. After Archibald had helped the Bogo Matassalai, says the story, they and the Minimoys had given him a large amount of rubies in a show of thanks for helping them. After returning home, Archibald brought the Minimoys with him and lent them his garden as their home. According to the story, he gave the Minimoys the rubies to look after them until he needed them. Arthur has become enamoured of a picture of Selenia, the princess of the Minimoys.