The first two volumes of The League of Extraordinary Gentlemen had a pretty simple concept: Transplant the concept of a Superhero team to 19th century Britain using a literary pastiche of characters from that era. They were good comics, but not what I would call groundbreaking.
The Black Dossier is a completely different animal. The framing story is moves the League timeline ahead to late 1950s, sometime after the fall of Big Brother's England. Two mysterious figures steal the "Black Dossier" which catalogs all known information about the various incarnations of The League. A gadget loving womanizing spy named "Jimmy" (James Bond) and a young woman named Emma Night (pre-marriage Emma Peel) are sent to track down the thieves and retrieve the Black Dossier.
The framing story is not what makes this book so interesting though, its the contents of the Black Dossier itself which are sprinkled throughout the book. There is a Shakespearean "historical" play detailing the founding of the league by Prospero under the patronage of the faerie Queen Gloriana. A sequel to Fanny Hill detailing her sexual encounters with the Lilliputians. A Bertie Wooster and Jeeves story detailing their brush with Lovecraftian horror. Even an inset Tijuana Bible.
What is truly amazing is that in each of these segments Moore apes the style of the original authors. The Shakespearean section is written in iambic pentameter and contains numerous instances of Shakespearean style humor. The Bertie Wooster section could be a Bertie Wooster and Jeeves short story... if it didn't contain Cthulhu.
If I have one complaint about the book, it's that it is so densely packed with literary references that it is a difficult read. Not that its not worth it, but it reminds me a bit of what it is like to read Russian literature. In any case there is a great site that gives page by page Annotations. I highly recommend reading it through while referencing the annotations at least once.
Tune in tomorrow for #3 on my Top Ten Favorite Comic Stories.