The plot concerns some mysterious events in a Russian space station in the future. The space station is studying the planet Solaris, which has a swirling plasma-like ocean that may or may not be sencient. A psychologist, Dr. Kris Kelvin, is sent to retrieve the remaining crew and determine whether the mission can continue. When he arrives, Dr. Kelvin is shocked to find that the crew has "guests." Whether the "guests" are hallucinations is left somewhat unanswered, and the ending is fairly enigmatic.