Tom Swift Jr. is hired by the U.S. government's space agency (NASA) to explore a comet. Using his recently invented telesampler, the youthful Tom aims to find new scientific facts about the next comet which passes near the Earth. In addition, Tom hopes to actually land on the comet. Tom has enemies who plan to foil the adventure. The Brungarians plot a scheme which will threaten the international scientific reputation of the United States.
At the same time, a series of unusual "UFOs" are streaking across the atmosphere causing the American Department of Defense grave concern. The adventure of TOM SWIFT AND THE MYSTERY COMET tells the story of how Tom both discovers the mystery of the UFOs and races to the deadly comet to save Earth from a perilous fate.