Rasselas and his siblings, the children of the emperor of Abissinia, are secluded in the “happy valley.” They are not able to leave this staggeringly beautiful place until the line of succession calls forth the eldest son, Rasselas,. However they are given everything they could ever desire and are shielded from the world’s miseries.
While most of the siblings enjoy their pampered and easy lives, Rasselas begins to feel a sense of ennui. He wanders about the forest, bemoaning the tedium of his life. Some of the sages sent to the palace to educate the siblings try to reason with Rasselas, but the young man remains desirous of seeing the wider world.
One day Imlac, a learned man, reads a poem to Rasselas and his siblings, which sparks an interest in Rasselas to hear more from the man. The two converse for some time, with Imlac imparting his history about how he ended up in the happy valley. He relates his travels around the world and his interactions with all manner of people, and how weariness brought him here. Rasselas is prompted to confide in him his own desire to escape, and Imlac says he will aid him and leave with him.
The two men labor to find a way out of the valley, finally succeeding with a pathway through the mountain. Right before they leave, one of Rasselas’s sisters, Nekayah, confronts them and explains that she had followed them and would also like to leave. Rasselas is overjoyed, and both brother and sister plan to depart.
The escape is made - Imlac, Rasselas, Nekayah, and Nekayah’s favorite, Pekuah, make their way out into the world. The brother and sister are startled at how the people they are soon surrounded with in the cities do not pay homage to them as royalty, but Imlac endeavors to keep their true identities secret.
They travel to Cairo, where they purchase a house and establish themselves. Their wealth is notable and other elites embrace them. After a few years Rasselas decides that he must spend time investigating what brings about true happiness, and when he discovers this, he will know what his “choice of life” should be.
Rasselas begins experimenting with different types of lifestyles and converses with a variety of individuals. He first spends time with young men, but finds their excess distasteful. He listens to a philosopher who advocates the eradication of all emotion, but finds the man incapable of living out his own proclamations when his own daughter dies.
Rasselas also observes the difficulties for those in power and a hermit who does not actually relish his solitude anymore. He and Nekayah spend time with the wealthy and within families, respectively, and discuss their findings. Rasselas notes that men in high stations are paranoid and caught up in plots and betrayals, while Nekayah deplores the problems she sees between parents and children. The two wonder whether marriage is better than celibacy, and why parents and children come into such conflict.
Imlac, ever the guide and counselor of the siblings, encourages them not just to debate but to go out into Egypt and visit the monuments and ruins. Rasselas and Nekayah wonder why looking at ruins and talking about historical figures are relevant to them. Imlac explains that the past is crucial to understanding the present, and one can never truly understand men without looking at their works.
The next day the philosopher and the siblings, accompanied by Pekuah and a train of servants, travel to the pyramids. Pekuah is afraid of the spirits of the dead and remains outside. Inside, Imlac lectures on the reasons why the Egyptians built the pyramids.
The pleasant afternoon is spoiled when, upon returning to the tents and train, the siblings and Imlac are told that a band of marauding Arabs abducted Pekuah and some of her maids. Turkish horsemen tried to pursue but could not. Private investigators and appeals to the government return no information.
All are distressed, but in the days and weeks that follow Nekayah sinks into an intense depression. She tells her brother and Imlac that she plans to live in solitude and wait to die. They counsel her not to let this one sorrow take over her whole life, and Rasselas asks if she might not wait a year to exhaust all possibilities of finding Pekuah. Nekayah agrees, and as time passes, begins to regain some joy in life.
Seven months after the abduction, word reaches them that Pekuah has been found. Ransom is swiftly paid, Pekuah is restored, and all rejoice. She tells them her story, explaining that her Arab abductor was kind and taught her much about astronomy. He never used her ill and only planned to extract money from her people.
Rasselas decides he wants to devote his life to learning. Imlac concedes that this is an admirable choice, but tells them the story of a learned friend of his. He knew an astronomer of great wisdom who worked in solitude and knew more than nearly anyone else about the skies. He visited this man and they became close friends. Imlac assumed he was the happiest of all men, but soon saw that his friend labored under some private worry.
Finally, the astronomer confided in Imlac that he was worried because he had a task that he needed to give to someone else. Imlac encouraged him to continue, and the astronomer sighed that he has the sole power to control the weather. He explained how years before, as he spent more and more time alone studying the heavens, he dreamed of having the power to control the rains and winds. One day he discovered that he actually could do this, and was shocked. He tried to reason with himself, and knew he could not prove it, but took on the weight of this task.
Imlac listened politely and agreed to help the astronomer with his task. As Imlac relates the story, Rasselas appears grave and Nekayah and Pekuah stifle laughter. Imlac chastises them that they cannot mock mental illness, as it is very common and the result of prolonged withdrawal from the world.
The girls are intrigued by the astronomer and endeavor to meet him. Pekuah suggests that she apply to be his student, and continue her studies she began with the Arab. The astronomer assents to this, and lessons begin.
Over time, the astronomer begins to enjoy the pleasures of this world more, and tells Imlac that the mist of his mind is clearing.
The rains come and the group is confined to their home. They discuss plans for the future. Pekuah wants to retire to a monastery, Nekayah decides to continue her education and start a college for women, and Rasselas contemplates running a small kingdom.
Once the rain ends, they realize their dreams are unrealistic and plan to return to Abissinia.