Before I continue I should point out that a really crappy movie was based on this series. This is a billion times better. Its the difference between Disney's Cinderella and one of those cheap knock-offs you find in the $1 on VHS at Toys R Us.
Anyways, The first volume is about a battle with FuManchu. The Second volume is about a Martian Invasion (as seen in War of the Worlds) the third is set in about 60 years after the invasion.
This third volume, "The Black Dossier" is about a book that contains information about the founding of the organization, the original team (including Prospero from Shakespeare's "The Tempest") and other members over time. The book is very experimental. It is very different than the 2 previous volumes. I'd recommend reading them first. I'd say more about it, but I do not want to ruin it.
The series is very literate. It uses all sorts of characters from books like Gulliver, Natty Bumpo, Fanny Hill, Pollyanna and many more. Some of these are just cameos or referenced.
I should point out that it is a graphic novel. It is not for kids. Your local library probably has it.