When an approaching comet threatens Earth, a small group of astronomers grapple with the question: warn the world, or keep silent? Comet centers on the Minor Planet Center (MPC), an international organization based in Boston, which acts as the worldwide repository of information about comets, asteroids, and other natural satellites. Members of the MPC serve an important purpose not only as a scientific body, but as one preoccupied with planetary defense; if an asteroid or comet ever threatens Earth, the Minor Planet Center will be the first to raise the alarm. Comet envisions a scenario where an event like this occurs, leaving the fictional members of the MPC to grapple with the choice of sharing the news with the world, or concealing it.