The gang infiltrates the spookily empty Darkwood High School. They find aquariums full of strange pale, translucent blind fish with squidlike tentacles. The faculty objects to their inquiries, and as they all shamble out of their darkened schoolrooms, it turns out they’re all vampires! All of them. The mob of vampire teachers closes in, and Excellence manages to break a window and steam some of them with sunlight, while Juliet stakes the rest.

Then Excellence demonstrates super-strength and hostility, as though she’s become the next Slayer. Juliet isn’t aware of having been dead, but there was that unfortunate Halloween when everyone became vampires, which may have qualified her as dead enough to call another Slayer. Excellence, in addition to rejecting the whole work-killing-vamps-till-you-die ethos, is wildly aggressive, knocking Walker across a room just because she suddenly decides he’s creepy. Juliet and Excellence fight, in a battle of Slayers, and Diligence uses a spell to freeze Excellence’s dress in time, making her immobile. A spirit of a dark-skinned woman clad in white wrappings, with wild matted black hair, white makeup across her eyes, and a stone knife in her hand, tears herself free from Excellence’s body. She threatens to kill everyone in the room, and Juliet attacks. The ghost smiles, and leaps, and she and Juliet merge.

Juliet doesn’t feel any different, she says. Oh, and there’s a vampire three miles outside town who needs to be slain. See ya!

A prayer vigil at the school is devoted to the worship of Cthulhu. Squid-monsters are handed out to students, who put them on their faces and allow their tentacles to reach down their throats.

Billy and Excellence break up the prayer meeting with an armored car equipped with a steam cannon from the Thirties. Three of its leaders are vampires, including Howard Porter, town librarian and noted anti-Christian activist. Billy boils him pink with steam, but it takes the stake to finish him off.

The rest of the Slayer gang head down to Fells Point, where Cthulhu itself is rising from the sea, ponderously heaving its massive bulk out of the water and onto the groaning land! Fighting it is obviously futile; just looking at it sends Alexandra, Dr. Armitage and Diligence insane. Juliet attacks, kicking and stabbing, but there’s nothing doing. So they follow Walker into the dreamtime, where Cthulhu’s real essence lies. Dr. Armitage theorizes that the cultists are trying to help Cthulhu, whose existence is spiritual, drain his essence into the physical world, organizing mud and seawater into a colossal physical body with which to inhabit the material plane. If it’s not stopped, it may well use up all the seawater in the world and have to start on the blood of the human race. Even if it doesn’t, it will ravage the Earth without let.

So they find their way to the dream-dimension Cthulhu rules, or more precisely fills from edge to edge with its vile green steaming nightmares. Diligence and Alex try sorcery on Cthulhu, causing it all sorts of hardship, but Cthulhu is adept at this game, too, and our heroes have to quickly use all their efforts to counteract the myriad hideous sorcerous attacks Cthulhu launches at them. Juliet has no sword, of course, but a voice behind her head says she doesn’t need a sword, and shapes her hand into a spear shape. Juliet steps forward, lunging, and her hand goes right through Cthulhu’s head, splitting it apart. Cthulhu is killed.

The body on the material plane sags and collapses, sliding back into the sea.

The Creel family invites our heroes to a good old-fashioned fish fry. As they’re all Deep Ones, they have lots of fish, all different kinds, and more relatives than most people were aware of. But the party is crashed by black-skinned fishmen with machine guns. Juliet attacks them, beating some up, and Diligence gets hold of one of their radios and calls for pickup. Juliet pursues one of them back to an underwater lair under the Miskatonic River; a fellow named Commander Stamp is running a secret Navy operation which turns men into hybrid sea-soldiers. They wanted to wipe out the Creels, whom they see (with some justice) as inhuman monsters. An invisible girl appears, sort of, and takes Juliet prisoner. She was recruited out of high school, as many such invisible people are. Juliet remembers Buffy saying she faced one once.

Everyone else arrives and tries to break in, getting in a tussle with some fish-commandoes. Juliet breaks free, takes Stamp captive, and makes him disarm his men. Turns out he’s not in the Navy any more; his command, SpecSeaCom, lost its funding in 1989. Melody, the invisible girl, gets away, but Stamp and his men are prisoners. Juliet doesn’t want to just let them go, but instead turns them over to the Watcher Council, which could use a few good frogmen.

A monster breaks free from a huge box of earth being mailed to Arkham. Uh-oh. But there’s a prom to attend, so no one gets all out of line. Juliet settles on red, after considering midnight blue and royal blue, for her prom dress; Excellence chooses lilac. Juliet goes with Walker, Excellence with Billy. Alexandra and Diligence spar for 45 minutes over whether he’s taking her to the dance or if they’re just going in the same car but not together, or what.

But then the monster shows up and tries to kill Juliet. It’s actually worse than that; Drusilla is back in town, still looking for the Slayer, and she finds her, finally. The Maletherium, a very bad man indeed, is coming to kill the Slayer, but once he’s done, he’ll eat up all the vampires for dessert. Chomp chomp chomp. So Drusilla wants to capture the Slayer and drag her out of town, to somewhere there aren’t any vampires. Like Cleveland.

Instead, Juliet appears hostile to Drusilla, just because she kills people to dress her dolls up. So Drusilla runs, and waiting for Juliet in the parking lot is the Maletherium, a huge, muscular hulk of mismatched flesh and gristle who yells everything and can sense her blood. He sensed it when Buffy drowned and Kendra was called, making two Slayers on the Earth at once. He sensed it when Juliet became a vampire and Excellence was called, making three. This has got to stop, he roars! He was made to slay the Slayer, but now there are three of them, and it’s time to finish the job, or at least this part of it.

Juliet stakes him real good. And it doesn’t work.

So she leads him away, hoping to drop him into the Hellmouth. He follows, pushing cars out of the way. Walker gets the crap pounded out of him – the Maletherium isn’t very quick, but oh my God he’s strong. And tough. Billy tries all sorts of dirty tricks and they basically don’t work.

Meanwhile, a teen faints on the dance floor (the theme was 2001: A Space Odyssey, and Excellence put $20,000 into decorations) and Diligence determines she was blood-drained. Diligence and Alexandra find and confront Drusilla – they use sorcery, she uses speed and fangs, then it turns out Dru knows a bit of sorcery herself and nearly sets Alex’s blood on fire (fortunately, one of Diligence’s powerstones catches fire instead) but finally a particularly painful use of Create Wood causes a near-miss stake in Drusilla’s side to sprout thorns – thousands of ‘em – all over her body. Alex magically draws the blood from Dru’s body, shriveling her, and she flees in panic into the alley, where Walker rips her apart.

Is Drusilla truly dead? Well, it’s hard to say. Which means no.

But Dr. Armitage is huffing and puffing up the road after Juliet and the Maletherium, whom she refers to as "bad-idea guy," believing that Maletherium means "bad theorem." Dr. Armitage stops to correct her Latin, and Billy ducks into the old shack where they first met Marshal three years ago. There is a bronze sword of simple design stuck into the floor and into a stone beneath it. Billy tugs and tugs, but can’t get it free. He hands it to Juliet, who draws the sword from the stone and chops the Maletherium into five unequal parts with it. Unfortunately, they start clambering back together.

Excellence calls some of the workmen who put up the big black monolith outside the prom. They try to hack the Maletherium’s terra-cotta parts apart with an ax and a jackhammer, but its detached arms try to strangle them. Billy finds a bucket of paint thinner in the truck and drops the Maletherium’s head into it. He suddenly cries out and is silent, and his parts fall apart.

Dr. Armitage explains that the Maletherium was a golem, made by seven Tzimicze lords to destroy the Slayer. He has no heart, but has a word written on a slip of paper in his head which contains his essence. When the paint thinner dissolved the ink in which the word was written, poof, he died.

Dr. Armitage also thinks the Maletherium was going to throw Juliet in the Hellmouth while still alive, which would prevent a new Slayer from being called. It might have ended with a wrestling match at the lip of Hell itself. But it didn’t.

Everyone graduates, even Billy, and Juliet is given a special Defender of Arkham award by Dr. Armitage and the school’s new principal, Coach Mundy.