In this hardbound edition of novel 23 in this series, Tom must travel to Mars to find out just why the small moon, Phobos, has suddenly begun coming close to the surface. In fact it is coming down to lower and lower orbits that could, within months, endanger the colonists on the planet below. He first tries to use brute force and to push it back into higher orbit, but nearly loses several spacecraft in the attempt. So, he now is faced with finding out the why of it all before he can find a solution that won't mean simply destroying the moon. That, he fears, might backfire and do damage to the colony and the planet. He tries to find some answers with the aid of his Space Friends, but they seem to have disappeared from his life. Without their help he mounts an expedition of Phobos and finds about the last thing he might think of. Now it is a race against time to see if he can rectify the situation and re-place Phobos in its correct orbit.