After an exhausting day at school, Peter Talbot arrives home and Singh announces him that he has a letter. Peter is surprised when he sees that it is an invitation to a party, organized by the Vampire Lord Seth. The invite stated that he could bring guests. Though skeptic, Peter decided, after talking to his grandfather, to go, taking his Pack with him.
Meanwhile, after a hard day dealing with the press and all the rocks thrown at him, the Vampire King Alucard returns home, and receives the same invite. Opening a secret door, he goes to a secret cavern under his house. There, he meets with his coven, the Nightwalkers. They have been watching Seth for a month now, and they suspect he is up to something vile. The members present, including the team's ”butler”, Salazar, decide to go, formulating a plan in case things go south.
The night of the party arrives, and the two teams are driven to the party by their respective drivers (Singh and Salazar). Before entering, Alucard tells Salazar to remember the plan. He nods and drives off.
Inside, both the members the Nightwalkers and the Talbot Pack spread out and start socializing with the various guests at the party. Mina Tepes was one of those guests. At one point, Peter and Alucard start conversing about a variety of things.
As they were talking, Mina notices them, and sees something vaguely familiar about the one standing next to Peter. As she approached them however, some younger vampire stops her and ask for her autograph. She signed it, but when she turned, the person is gone (Alucard having been called by Claire), and Peter was talking with Mikey instead.
Nothing out of the ordinary happened as the night progressed. Then, Seth climbs on a platform, to make a speech. However, unseen by anyone, machinery starts moving behind the platform. During his speech, he apologized to those present, saying he has to do what is necessary to save his species. Just then, a force field covered him, and a large machine appeared behind him. Suddenly, what appears to be energy is absorbed from every vampire and werewolf in the room. Both the Nightwalkers and the Talbot Pack are rendered helpless, until Salazar arrives there on time and destroyed the machine, leaving only a piece of it intact. The two teams immediately get up and start approaching Seth, asking him the reason behind his actions. Seth angrily responds that he has to do what is necessary to save his race, revealing that he intended to use the gathered essence to turn himself into a Kinsmir, and rule vampires into a new age. Alucard immediately steps up, telling him that violence and conquest was not the answer, and that only through peace can vampires prosper. Seth denies this, and prepares to escape with the remaining piece, summoning Ghouls to keep the two groups occupied.
Part of the Pack, along with Alucard, Neo and Claire deal with the Ghouls, while the rest and a recovered Mina dealt with Seth. Alucard tries to cut the Ghouls, but they would instantly regenerate. Worse, if they were cut in two, they would clone themselves and blunt force was just as unsuccessful, as broken bones and twisted limbs would instantly repair. The rest weren't having any luck either. Just then, Nathan Forge had equipped the Dark Knight Armor (which he had summoned previously), and attacked the Ghouls with concentrated UV light, weakening them.
During this, Seth recovered something from the destroyed machine. Mina and the rest tried stopping him, and were succeeding. But then, both Mina and Seth grabbed on the part the latter had recovered from the machine. Seth declared that Mina had grabbed the "wrong end", and turned the part on, absorbing Mina's essence at point blank range, severely weakening her. Then, gathering his minions, he retreated.
Neo was quick to tend to Mina, allowing her to drink his blood, but would still be unable to fight.
Meanwhile, Alucard was exchanging information with Peter on the situation, and they decide to collaborate to take down Seth.
Back at the Night Cave, the Nightwalkers and the Pack were comparing notes (Christie had stayed behind to look after Mina, who was still weak). Kylie told everyone present, that she recognized the crystal in Seth's machine from a legend she had heard. Using the computer, she indeed found information on a crystal called "the Essence Stone" which, according to legend, could absorb the vital essence of anyone who touched it. Salazar confirms that he had heard rumors of such a stone. Nathan then shows everyone reports of stolen technology from different firms, and some from military sources. Analyzing the stolen technology, Nathan discovers that Seth is planing to build a huge vitality absorbtion machine, as well as a power amplifier, capable of extending the Essence Stone's influence for miles. The only thing he needs to complete the machine is the Power Amplifier, which can be found in only one location: Bio-Tech Labs.
Acting quickly, Peter calls the M.O.N.S.ters for help, while Alucard and the Nightwalkers prepare for battle.
They arrive at Bio-Tech, only to find that the M.O.N.S.ters where already fighting the Ghouls. With their teams rushing in to help, Peter and Alucard face of against Seth. A fierce battle ensures, with neither side besting the enemy.
However, the fight abruptly ends when an infiltrator, disguised as a scientist, steals the Amplifier (despite the best efforts of Fly-Girl, Dru, Derek Xander, Tom Sizemore, Claire Nightshade and Cole Walker). The Ghouls and Seth then retreated to complete his machine.
As the three teams treat their wounded, and contemplate on what to do next, Alucard receives a message from Hal, who had scouted ahead, and had discovered that Seth had installed the machine in Everett central park, being the perfect location for the absorbation to take place all over the city
Alucard proposes that they all split into three teams: The heavy hitters deal with the Regenerator Ghouls, The leaders (He, Peter and Vincent Celeste) deal with Seth, and the rest will try to get to the machine and deactivate it.
A huge fight commences, the park turning into a war-zone. At one point, Christie and Mina join the fight, assisting the heavy hitters. During the fighting, Mina and Alucard briefly look at and recognize each other, and get so distracted that they are almost hit by their respective enemies. When they look again, they lose sight of each other.
During the battle, the machine was activated, weakening the Pack, Mina, and Alucard. All the others defended the weakened. The ground team managed to destroy the Power Amplifier, but Seth could still use it to absorb the essence of Alucard and Peter. He said that, since Peter was a Werewolf Alpha and Alucard was a Vampire King, they had all the essence he needed to become a powerful Kinsmir.
Just as Seth was gloating in his victory, Peter and Alucard, in a display of willpower that amazed everyone present, escaped the effects of the Essence Stone, and, while still drained of essence, activated their power-ups: Peter entered Beast Form, and Alucard Awakened. They defeated Seth and cleared the way to the machine. Alucard then pulled out the Essence Stone, and used it to absorb the essence of the Ghouls present, turning them to dust, then dropping the gem and both of them fainting from the strain. The ground team then destroyed the rest of the machine.
Alucard and Peter soon recovered, and were cheered on by their respecting teams. Suddenly, Mina called Alucard's name and approached him. He suddenly started becoming nervous, something none of his teammates have ever seen him express. Then, to the amazement of those present, Mina called Alucard "brother". She emotionally started explaining how she and Alucard met, how he was adopted in her family, and how close they where. She then tearfully hugged him, and asked why he had left. Alucard didn't react at first, but he then explained that he had been afraid of what he had done and what he had become. He declared that he had spent the last 400 years truing to make up for that sin. Hugging her, and crying real tears (not blood for the first time in a long time) he asked her to forgive him. She answered that she already had, and the two hugged, tearing up all those present.
The next day, Alucard threw a huge party at Leather Wing Manor. The Talbot Pack, including Sir John and Singh, were present, alone with the M.O.N.S.ters and their associates, and of course the Nightwalkers.