The Commissar Vanishes is a book about what happened to many people in the Soviet Union between the 1920s and 1950s. During this time, the Soviet Union was ruled by a dictator known as Joseph Stalin. Stalin wanted all people to follow his rules and stay loyal to the Soviet Union. To make sure this happened, he set up a group of people in the government called the commissars to watch over everyone and make sure they didn't break any of Stalin's rules.
If someone was found to be breaking the rules or not supporting Stalin and the Soviet Union, the commissars would make them "vanish" -- usually this meant they would be put in prison, or worse. Over the years, hundreds of thousands of people this way by the commissars.
The Commissar Vanishes is a book that tells these stories: it documents the stories of all the people that the commissars made "vanish" in the Soviet Union.