Raz (Erasmus), the protagonist in the novel Anathem by Neal Stephenson is a mathematician and monk (a "fraa" or "avout") in a monastery on the planet Arbre. Thousands of years prior to the opening of the story, Apert's society was on the verge of collapse, and the avout fled into monasteries in order to protect the cultural and intellectual legacy of their planet.
The novel opens at the beginning of Apert, a periodic festival during which the monastery is opened to the public. Raz is summoned by powers in the outside world to help them explore an alien ship in orbit around Arbre. Raz's mentor, Orolo, used a telescope to peer at the ship, which is a violation of the order's rules, and he was ostracized from the monastery. The ship shines a light down on to the planet, which may or may not be an attempt to communicate with the inhabitants of Arbre. Raz and his fellows travel to a distant monastery, but Raz tries to find Orolo first. He eventually finds Orolo, and they travel with others to another monastery, where they encounter one of the aliens, called Geometers, who has been killed. The leaders of Arbre meet with the monks to discuss the aliens. The aliens are eventually found to come from alternate universes. Apert's leaders also uncover an internal conflict among The Geometers, and lauch an attack against them. The monks are drafted into the attack.
Alternate universes, potentially hostile aliens, banned technology, attempts at cultural preservation...Anathem has it all! What happens next? Read and find out.