BombDown - science fiction romance, #2

Staying at a hotel out of town to attend a wedding, Monroe is asked by two kids to run after their mother, who may be a spy. At a nearby submarine base, Donna is asked to speak to a scientist about a plan to shoot down an asteroid. Still in grad school, her new job doesn't offer much in the way of good looking guys, but what about Geoffrey? He's new. But there's little time to study this. North Korean and South Korean subs are firing nuclear warheads at the asteroid.
The North Koreans will be darned if the South shoots it down before them.