Timothy Penn led a very regulated life. He worked as an assistant clerk in a bookstore and he spent time reading in the park. But he was fascinated by the news of the possible existence of a planet in Earth's orbit but on the opposite side of the Sun. And then when he won the largest dividend ever awarded in a national football pool, he did something that would completely overturn his humdrum existence. He purchased a passage on the "Skylark", a spaceship bound on a trip around the Sun to see if that other planet really did exist.

Timothy not only found adventure but romance in the person of Rose Pollenport, the beautiful daughter of the world famous scientist in command of the expedition. The planet on the other side of the Sun, which they called Antigeos, was a strange but intriguing place, with inhabitants that seemed both very human and very alien. And Timothy's adventure was only beginning when they landed.