The story begins as the members of ER-2 go on a routine exploration mission while Popov is left behind to oversee the construction of a permanent base for the arriving colonists.
It takes a few hours for Popov to locate the robots, fix them and set them back to work.
As the team has breakfast the following morning, a figure of a 13-year-old human boy appears on the base.
Another message arrives that identifies the spaceship that ER-2 discovered as Pilgrim and the two pilots as Alexander (Russian short for this name is Shura) Semyonov and his wife Maria-Luisa Semyonova.
There is no direct connection between the antennae and the aliens, but the newly discovered race is named Ark Megaforms.
He allows the humans to study him and question him about his foster parents in exchange for the promise to leave.
The communication does not proceed smoothly as the Kid exhibits the mixture of human and alien psychological traits.
Frustrated with the lack of progress the humans give the Kid a portable video transmitter.
They do not tell the Kid its function and hope that he will take it with him and the scientists will be able to track his movements outside the base.
Over the transmitter the humans see as the Kid walks to the wreckage of the Pilgrim, levitates to a distant canyon and proceeds into the planet's interior.
At this moment one of the humans - Maya Glumova turns on an emergency flashlight that is built into the transmitter.
Gorbovsky informs Komov that an ancient satellite was discovered orbiting Ark.
In the epilogue of the novel, Popov talks to the Kid over the video transmitter and reflects on the decisions made by the humans.
Boris Strugatsky admitted that the brothers did not like the title, which was only chosen as the official name because the publisher wanted it.