Professor Wedgwood leads the first team of Moon explorers, and is successfully launched into space. But when his supply rocket cannot take off by automatic pilot, the Professor's children volunteer to save the expedition... and find a stowaway.

When Professor Wedgwood's moon expedition is jeopardized by the failure of his automatic supply rocket, his children and their reporter friend come to the rescue. The two rockets fly into space. As they near the moon, a third rocket appears.. a spaceship from nowhere.

Professor Wedgwood's children have brought his supply rocket to the moon. But the rockets have landed 150 miles apart. Both parties discover that someone has already been to the moon.Then Jimmy disappears.

The three children find a cave containing relics of a previous civilisation. Meanwhile, Wedgwood is trying to reach them. Then the children make another startling discovery.

Professor Wedgwood's amazing discoveries on the moon indicate a previous landing sometime in the distant past. Will the alien spaceship reveal its secrets?

While Wedgwood and the children explore inside the ancient spaceship, meteorites bombard the Moon. When dlsaster strikes, Wedgwood is faced with a terrible decision.