Fraa Erasmas lives in the concent of Saunt Edhar on the planet Arbre. Concents are like monasteries, except they are devoted solely to the study of intellectual and philosophical matters rather than religion. The concents are closed off from the outside world in an effort to maintain continuity and preserve the knowledge gained inside. They open their doors for a single day at one, ten, a hundred, and a thousand year intervals.
Over the centuries the outside world has suffered through cycles of rise and collapse, with revolutions often ending in attacks on the concents in the superstitious belief that they harbor secret technologies that can be controlled with the mind. The governments have a strict policy of not allowing the concents to own or develop technology, and can summon their members for questioning at any time.
Erasmas is happy in the concent and enjoys the pursuit of mathematics and philosophy, having long discussions with his friends and teachers. But on the eve of one of the days the doors are to be opened, his main teacher Fraa Orolo, is banished for using prohibited technology. Erasmas and his friends sense that there is more to this and soon discover that Orolo has uncovered a shocking secret; there is an alien spaceship in orbit around Arbre.
Pursuing the investigation secretly in fear of being banished or punished by the outside government, they eventually figure out that the government is also aware of this ship and trying to cover it up in fear it will destabilize their rule and cause panic.
Aside from the investigation, a large part of the book is dedicated to the philosophical discussions between Erasmas and his friends and teachers. His main area of interest is regarding theories about parallel worlds and the potential of being able to shift between realities with the mind alone. This ties in with the superstitious beliefs of the general population about the concent residents having secret technologies.
Time passes and Erasmas is no closer to finding what happened to Orolo when the government suddenly summons several of his friends. Erasmas is devastated, since it is unlikely they will ever return, but shortly after that the alien ship makes itself known by shining a laser on a another concent.
Erasmas himself is then summoned and finds himself traveling with a small group to make contact with the ship. They travel by foot and have to avoid mobs of scared civilians and inhospitable terrain. At one point Erasmas splits off to find Orolo and succeeds. While with Orolo a shuttle from the alien ship lands with a dead crew member inside, revealing that the aliens appear to be human. Orolo and Erasmas investigate the technology and biological information until their location is attacked from the spaceship and they have to flee.
Orolo dies in the attack but Erasmas continues on to his original destination and finds most of the previously summoned people there, along with government and military leaders and members of many other concents. They are all required to work together to make contact with the ship and find out if its a threat. But Erasmas is much more interested in where it came from in the first place.
Best part of story, including ending:
The worldbuilding and philosophical discussions are fascinating and very well developed, it makes you think a lot.
Best scene in story:
When the aliens attack by dropping a rod from space and causing the volcano to erupt, it's a great action scene in an otherwise very cerebral book.
Opinion about the main character:
Erasmas is intellectually curious, which makes being inside his head very interesting.