General Toda Rai, the Rajput ruler of a princely state in the Himalayas, invites the Congregation of The Servants of Mary to establish a school and hospital at Mopu, a dilapidated palace situated on a high cliff. Several monks previously failed to start a school there; the general's agent Mr Dean describes the social and environmental difficulties the sisters will face. The ambitious Sister Clodagh is appointed Sister Superior and is sent with four other nuns: Sister Philippa for gardening; Sister Briony for the infirmary; Sister Blanche, better known as "Sister Honey", to teach lace-making; and the emotionally unstable Sister Ruth for general classes. Mr Dean is unimpressed and predicts the women will last only until the beginning of the monsoon.
While setting up the convent, the sisters face difficulties with the old palace and also the local population, often clashing with the native caretaker, Angu Ayah. They have difficulty accepting a Hindu holy man in their grounds (the general's uncle) who spends all his time in meditation on one of the mountains. The sisters take in Kanchi, a local girl, to try and control her erratic behavior, and they also tutor the general's heir—referred to as the Young General—in Western culture prior to a trip to Britain. Ayah whips Kanchi for stealing, but the Young General stops her. He soon falls in love with Kanchi, creating a situation that Mr Dean compares to the tale of The King and the Beggar-maid.
Each convent member begins experiencing ill-health and emotional problems caused by their surroundings. Philippa loses herself in the environment and plants the vegetable garden with flowers. Ruth, already highly strung, becomes increasingly jealous of Clodagh and obsessed with Mr Dean, leading her to renounce the order. Clodagh recalls a failed romance which prompted her to join the order. Honey's growing attachment to the local children ends disastrously after she gives medication to a fatally-ill baby. The child's death angers the locals, who blame and abandon the mission, putting further strain on the sisters. Mr Dean fails to persuade Clodagh to leave before anything else untoward happens.
One night Clodagh confronts the now-unstable Ruth, finding her wearing a modern dress she ordered to entice Mr Dean. Ruth escapes Clodagh's watch and finds Mr Dean. When he rebuffs her advances, she suffers a mental breakdown and returns to the mission, intent on killing Clodagh. When Clodagh rings the morning service bell, Ruth attempts to push her over the cliff edge. In the ensuing struggle, Ruth falls to her death. The mission leaves just as the monsoon season begins, with Clodagh's final request to Mr Dean that he tend Ruth's grave.
