What's the plot of MW2?

I'm probably one of the few people who never got to play Modern Warfare 2, but I did play Call of Duty 4: Modern Warfare. Now I bought MW3, but I'm worried I might be a little lost on the story. So I'd just like to know the basics of the MW2 plot before diving into MW3, no extensive answer necessary.

Assuming I remember the ending of MW1 (and my memory doesn't fail me), what big events moved the plot in MW2? I just want to catch up on the story I missed, please don't say anything about the story of MW3.

In order words: spoil MW2 (but not 3) for me.

You can read a quick synopsis from Call of Duty: Modern Warfare 2's IMDB page

Five years after the events of Call of Duty Modern Warfare, Russia has been taken over by the Ultranationalists and an Ultranationalist rebel by the name of Vladimir Makarov carries out terrorist attacks against the West. A CIA agent is put in the ranks of Makarov, but after being killed during a terrorist attack, the Russian government believes the US ordered the attack and invades the US in retaliation. The story focuses on a US Ranger that takes part in repelling the Russian invasion, while a multinational task force seeks to find Makarov and put an end to any further damage.

There is another major story beat to the game in the form of betrayal by a disgraced military figure, but it doesn't have a significant impact on the overarching plot of Modern Warfare, Modern Warfare 2 and Modern Warfare 3.

You can read a much more comprehensive retelling of the game's plot by visiting Modern Warfare 2's Wikipedia page