At the center of the story is Charlie Haskell, the U.S. vice president, who in 2024--an election year--has arrived at the American Moonbase to cut the ribbon and declare it operational. But there's a problem, and it's a doozy: a "sun-grazer" comet, with immense mass and speed, is on a collision course with the moon. Haskell, with an eye to his public image, puts himself at the bottom of the evacuation list. But time grows critically short, and soon more than his political future is in jeopardy--broken chunks of moon will begin exploding outwards. If they reach Earth, some of the chunks are big enough to cause an extinction event.