An object is on a collision course with the moon.
It hits the moon, causing a major explosion.
The aftermath of the explosion with a debris field around the moon. A woman astrophysicist is interviewed about what has happened and if it poses any danger to the Earth. She realizes later that something might be very wrong. First off, some of the asteroid fragments are going to hit the Earth.
The next major character to be introduced is an explosives expert who implodes buildings. (This is the kind of side story that makes a lot of sense and is not just a distraction.) Also, another good point for the movie, is that the female scientist works with a male scientist who, for once, does not put her down or shut her out.
It turns out the asteroid fragments are more dense than the scientists figured they would be, and the moon's orbit has been slightly changed. A lunar probe is sent out and detects lot of debris and is destroyed in the process.
The explosives expert is told by a military guy that he is needed, and 'refusal is not an option.' There's a geological fault forming on the moon that could destroy it and, thus, destroy the Earth. Now we have the guy who opposes who appear. The guy didn't care for her father and his theories.
Jets are able to destroy one of the larger fragments on a collision course with a city. Mexico City gets hit by several chunks of debris and is pretty much destroyed. They are going to have to launch a shuttle in a storm to go to the moon and do something that can fix the fault.
(Here's where some unrealistic things are happening. The incoming debris seems to only be hitting cities and missing all the areas that are not cities. The shuttle they are using isn't our normal shuttle, though, as it uses nuclear pulse engines plus it apparently can actually go as far as the moon and back.
The shuttle launches.
The shuttle gets near the moon, having to dodge a lot of debris.
The fault that has developed on the moon. It turns out the one guy who didn't believe the woman astrophysicist was wrong and so the shuttle has the wrong type of explosives on board. They will have to convert it to the type that might work, and then find where to set that off.
It's a decent film, avoiding the problem of so many disaster films that take up lots of time with useless side stories. The effects are also usually rather good.