In this hardbound edition of Tom's 16th adventure in this series, he finds out that a newly classified exo-planet outside Pluto's orbit is about to have a close encounter with the return of Haley's Comet. The problem is that at such distances nobody can tell just how close. A visit to the Planet, Eris, is called for but he must first devise a ay to travel faster than he ever has before so the trip can be accomplished before the pass by. What he comes up with astounds even his father, and that takes a lot! Tom, Bud and their crew arrive in time to witness a catastrophic collision that begins the slow and inevitable break up of the planet. But, trouble is brewing as calculations show some of the debris will eventually drift in and possibly collide with Mars and the Earth. What to do? Nobody has ever tried to put an entire planet back together. This is a Humpty Dumpty exercise of planetary proportions.