The super short version of this book is only two steps:
Step 1: Take Lincoln biography (or Ken Burns's The Civil War)
Step 2: Add vampires
We're done here.
Okay, okay. We'll elaborate. Sheesh.
The slightly longer version starts in 2010, when "Seth Grahame-Smith" (the character, not the author) gets the secret journals of Abraham Lincoln from the vampire Henry Sturges. The rest of the book is the story of those journals (and some interviews and probably some notes cribbed from Wikipedia).
We start with Abe Lincoln as a boy, unhappy with his father Thomas, and especially unhappy with the vampire Jack Barts, who killed his mom Nancy Hanks Lincoln. Thomas remarries, which makes lil' Abe feel a bit better (and stepmom Sarah is nice to Abe and even buys him a journal).
But Abe only feels better when he stakes Barts through the heart and swears vengeance against all vampires everywhere—not just the mama-killers. But Abe is nearly killed by the second vampire he tries to do away with, until he is rescued by the heroic, non-sparkly vampire Henry Sturges.
(We also get to hear about how Sturges came to America and became a vampire, which has to do with the mysterious disappearance of the Roanoke Colony. Except it's not so mysterious here: it was a vampire that made the colony disappear. Yikes.)
Henry trains Abe to kill vampires and keeps him updated on what evil vampires need killing. Abe meets other friends—Jack Armstrong, Joshua Speed, Edgar Allan Poe, Ward Hill Lamon—who help him hunt vampires or tell him about vampiric history.
(In case you're curious, the short version of vampiric history is that vampires love America because (1) Europeans vampire hunters got too good at their job; and (2) the American slave system is an easy way to feed.)
Abe learns firsthand that vampires hide in the South behind the mask of slavery. So vampirism and slavery go together like peanut butter and jelly. If he wants to destroy one, he'll have to destroy the other. Luckily, Abe has always been an abolitionist, just like his dad. Phew.
Abe runs for political office a few times (loses some, wins some others). He also falls in love twice—the first time with Ann Rutledge (killed by vampires), the second with Mary Todd (whose dad is an ally of vampires, but Abe decides he can live with that).
When Abe and Mary marry and have kids, Abe retires from vampire hunting. Also, Abe is tired of politics, so he goes back to just being a regular old lawyer. But Henry lures Abe back in to the vampire-slaying business (it's more of a hobby really, since no one gets paid) and lays out the problem: the bad vampires want to make a war between the North and the South. Uh oh. Shmoop smells trouble.
To prevent all this Badness from going down, Abe runs for president, but first he goes to assassinate the human Jefferson Davis with his friends Speed and Lamon. They fail, but thankfully, Henry and some good vampires save them all from the bad vampires who are more than a little ticked off.
And luckily Abe still gets elected president (without any help from vampires, we are assured). Then the South secedes and we have a Civil War. It's kind of a big deal. It's a big war and lots of people die, as we know from history class. What we never learned in history class is that the Confederate army includes vampires, who are very good at scaring Union soldiers. Also, a sneaky vampire poisons Abe's favorite son, Willie. Hey, it happens.
To counter the Confederate vampires, Abe issues the Emancipation Proclamation, freeing the slaves in the rebel states. So some of the slaves rise up against the vampires. Which helps the North, and (Spoiler Alert!) the North wins.
But then, (Spoiler Alert!) Lincoln is assassinated by John Wilkes Booth, who is both a Confederate sympathizer and a vampire. Henry Sturges tracks Booth down and kills him just before the soldiers get to him.
And then (Okay, actual Spoiler Alert!) Sturges turns Lincoln into a vampire and they spend the rest of their lives fighting against the Ku Klux Klan (vampires) and Nazis (probably also vampires).