Although Aldea has hidden itself from the universe behind a sophisticated shield, it's soon apparent that the discovery was no accident. Having lost the ability to reproduce, the Aldeans kidnap several children from the U.S.S. Enterprise , including Wesley Crusher, to perpetuate their race.

When hostage negotiations fail, Picard struggles to find a method of penetrating the planet's shield while Dr. Crusher studies the cause of the Aldean sterility problem. Meanwhile, Wesley uncovers the key to the planet's sophistication-a computer known as the Custodian, whose power source is unknown even to the Aldeans.

Before long, Dr. Crusher discovers that the Aldeans are suffering from radiation poisoning caused by the protective shield overhead. As it turns out, the shield has also weakened the planet's atmosphere. Picard and Crusher inform the Aldean leaders of this development and plead for the release of the children. When the Aldeans agree Picard uses the U.S.S. Enterprise to repair the planet's atmosphere. Crusher, meanwhile, gives the dying race a treatment that will save them.