The plot involves Quatermain going on a trek into Africa to find a mysterious flower.

Brother John, who has been wandering in Africa for years, confides to Allan a huge and rare orchid, the largest ever found.

Due to a mixup at auction, Somers ends up paying a huge sum for a particularly rare flower.

Stephen resolves to sell the flower and use it to finance an expedition to Africa to recover a live specimen of the huge orchid Allan brought back with him.

They meet Arabian slave traders, warrior tribes, cannibals, and a giant gorilla.