It is a disastrous day for Col. Raeburn when Tyro, the leader of the planet Neptune, persuades Raeburn’s secretary, Marla, to go to Neptune with him. The Colonel does not believe she has gone of her own free will and gives Dart the task of bringing her back.

When Dart and his crew make an emergency landing on Titan to repair their galasphere, they make a curious and far-reaching discovery.

Dart and Slim are invited to the planet of Lumen. On their arrival Dart's oxygen cylinder is pierced. The planet's only oxygen comes from blister plants in the "cave of death". Dart and Slim must find the plants before dawn, or risk being boiled alive in the heat of the Sun

Stolen art treasures are being transported into space. Raeburn suspects that Venusian millionaire Tara is behind the thefts, but his palace is too well guarded. Professor Haggarty develops a watch that speeds up the wearer's reaction times by a factor of sixty, which enables Dart to sneak into the palace unnoticed

Husky, visiting Mars with Larry Dart, becomes invisible through an accident. This proves of great value, but Husky does not want to be invisible for ever, and there seems to be no prospect of him returning to his normal state.

One of the lakes on Jupiter is found to contain water with extraordinary properties. This is of great interest to the scientists, but from being a matter of interest the water soon turns to being a matter of deadly peril to the planet.

The Tula Fish in the Venusian Magda Ocean are evolving at an extraordinary rate and attack fishermen. The Galasphere crew are sent to help and discover that routinely dumped building materials may be the cause of the Tula's accelerated evolution

While Dart and his crew are orbiting around Uranus, Husky sees a light on the planet which they learn is coming from the headquarters of the Duos, strange beings who inhabit the very heart of Uranus. The Duos, however, are in search of a less unpleasant atmosphere and decide to conquer Earth.

Colonel Raeburn and Haggarty are on a hunting expedition when Raeburn shoots down an object shaped like a bell. Although not a human being, the bell has a voice and proves to be very intelligent, especially when Dart is buried in a cave without food and water.

Col. Raeburn receives a message from Mars and learns that, as a result of terrible dust storms, the drought on the planet is getting worse.

No one believes Professor Zeffer when he tells them that he has picked up a message from Alpha Centauri, the nearest Star to our solar system. But when a strange being lands on Earth, it seems that the Professor’s story is not so fantastic.

Colonel Raeburn is faced with a dangerous situation when a would-be dictator sets himself up on the satellite Ganymede and begins to interfere with the sun.