Harry Dresden, Chicago's only wizard private investigator, must prevent three separate groups of necromancers from completing an evil ritual and becoming roughly as powerful as minor gods, killing thousands of innocents in the process. Harry Dresden is a wizard, strong enough to be on the White Council, but distrusted by his magical peers due to an incident in his teenage years when he used magic in self-defense to kill the sorcerer attacking him. So when a powerful vampire named Mavra blackmails him into searching for something called "The Word of Kimmler," and Harry realizes that several groups of necromancers are looking for the exact same thing, Harry tries to keep his fellow wizards out of the loop.
Harry consults with Bob the Skull, a spirit of intellect that once served Kimmler himself. Kimmler was a necromancer, a wizard who pursued power over life and death, and who became increasingly horrible over his long life, ultimately causing mass destruction during World War I and World War II. The White Council had to kill Kimmler seven times before it finally took, and even now, anything associated with Kimmler is immediately regarded with suspicion. It seems likely that "The Word of Kimmler" is one of a series of books he wrote, most of which have been destroyed, since they contain how-to instructions for a variety of nasty spells.
Harry starts looking for suspicious deaths, since Halloween is coming up, and anyone who plans to complete a major necromantic ritual All Hallows' Eve may also complete small rituals or sacrifices leading up to the larger one. He speaks with Waldo Butters, a medical examiner at the Forensic Institute, and learns of the death of one of mob boss Johnny Marcone's associates, a smuggler nicknamed "Bony Tony."
Harry and Butters are attacked at the morgue, which clues Harry in to the fact that Tony might have stumbled upon the "Word of Kimmler" or a similarly dark artifact. The necromancers involved seem to want Butters, specifically, as they believe that Butters must have found whatever Tony had on him at the time of Tony's death. After several serious confrontations with various necromancer groups, Butters is briefly captured, and Harry ultimately trades the one item they did find on Tony--a list of numbers--in exchange for Butters's freedom.
Between Harry's investigations into another book the necromancers seem interested in, and the revelation that the necromancers will be trying to summon thousands of spirits into the Chicago area on Halloween night, Harry finally realizes that the Word of Kimmler is effectively an instruction sheet for how to steal spirits' power and use it to become a functional god. When Bob the Skull is stolen, Harry realizes that even though the Word of Kimmler is missing, the information contained therein is already in the necromancers' hands, as Bob helped Kimmler in many of his rituals in the past.
Reluctantly, Harry calls in the Wardens of the White Council. Only five of them appear, and Harry learns that the Wardens have recently suffered terrible losses; they now have around fifty members left, out of more than two hundred original Wardens. They recruit Harry into their membership, and make preparations to disrupt the Darkhallow ritual that the necromancers are trying to perform.
Harry realizes, almost too late, that the numbers on Tony's list correspond to GPS coordinates, and finds the "Word of Kimmler" hidden in a museum. He learns that the only way he can close to the center of the Darkhallow ritual after it starts is to have necromantic energy surrounding him. And, well, he's in the right museum... so he animates Sue, the most complete Tyrannosaurus Rex skeleton ever found, whose fossilized bones are on display there.
With Butters's help, Harry rides the animated tyrannosaurus toward the Darkhallow, helps his fellow Wardens to fight off zombies and ghostly spirits, and then successfully disrupts the Darkhallow. Warden Luccio, the leader of the Wardens, is nearly killed by the necromancer called Corpsetaker, but survives after being transferred to a new body by Corpsetaker as part of a larger plan to fool the Wardens into letting their guard down. In the end, Dresden gives Mavra the copy of the Word of Kimmler that he found, but warns her that since he now knows how to turn himself into a god, she had better not try to blackmail him or threaten his friends a second time.
Best scene in story:
Frankly, Warden Ramirez and Harry Dresden riding through the streets of Chicago on the back of a reanimated dinosaur was pretty epic, and for pure action I'd say that one. For dark humor, there's an excellent scene much earlier in which Harry is trying to snap Butters out of a fear-driven paralysis with the chant, "Polka will never die!" Immediately after Butters has joined Harry in shouting that phrase, a pair of hands break through the window, reach down, and drag Butters outside into the middle of a bunch of zombies. It's a very tense moment that nonetheless manages to be funny, and it's something of a turning point in Butters' character development, because even though it ends badly, it is still one of the first times Butters snaps out of being frozen with terror.
Opinion about the main character:
Harry Dresden is funny, brave, true to his friends, and self-sacrificing. He lives up to his principles, even if that means he's likely to die. And he's very protective of the people he loves. Dead Beat is not the only book in which it's made clear that Dresden would sacrifice himself for his friends, but it's the first in which he explicitly says that he would be willing to seek power from evil sources to wreak vengeance on anyone who hurts the people he cares about.