Second-grader Alisa Selezneva, along with her father and flight mechanic Zeleny, sets off on an interstellar scientific expedition to collect rare animals for the Moscow Zoo. But the crew's seemingly innocent voyage in search of rare animals suddenly turns into a dangerous adventure. The girl and her friends must battle space pirates and solve the mystery of the disappearance of three legendary captains. This science fiction story, first published in 1974, remains immensely popular with young adventurers in Russia and around the world. It has been translated into virtually every European language, as well as Chinese and Japanese. The animated film 'The Mystery of the Third Planet' was based on the story.