Raimi credits the inclusion of Brock to producer Avi Arad, who until recently was the chairman and CEO of Marvel Studios. "He said the fans want to see Venom," Raimi says. "I come from a different generation. I read the comic books in the '70s, where it was Green Goblin, Sandman, Electro, Mysterio, the Vulture. It was not until the late '80s that Venom came about. But Avi said, 'I'm telling you, they're waiting for him. Don't be selfish. Spider-Man is everyone's myth, not just yours.' "

Tobey Maguire in Spider-Man 3.

Brock's transformation into Venom is the result of an alien "symbiote" organism that infects its host, making him more powerful but also unleashing his dark side. But first the symbiote latches onto Peter, who, because of his recent bloodlust for Flint Marko, is a receptive host. It stains Spidey's costume black before a subway action scene (Arad promises it will top the aboveground train sequence from the second movie) in which Spider-Man battles Sandman. The blackness enhances Spidey's powers while clouding his moral imperative to do as little harm as possible. "He can shoot webs farther, he can run faster, jump farther," Raimi says. "He's more powerful and unfortunately a little more careless."

Although Sandman and Venom have exciting and frightening powers, Raimi says it's their complex motivations to do evil that matter most. "I wanted to humanize the villains. Because it's really the story of Peter Parker learning that we're all sinners, and none of us are right or wrong."

Also riding the wave of complex emotions is Harry Osborn (James Franco), who has inherited the mantle of the Green Goblin from his father. Though Harry and Peter come to airborne blows, Dunst says that their conflict is essentially personal: "We're all trying to find ourselves in this film. The relationships — especially me, Harry and Peter — are full of history, and we could take the story to a much more intense level." She adds, "There's a lot more story going on in this one. I feel like every time we did a scene, Sam explained the entire film to everybody so that we'd all understand where we were at."

To realize his vision, Raimi drew from both likely and unlikely sources for the casting. "Gwen Stacy is this buxom blond, and I'm this red-headed character actress," says Howard (The Village, Lady in the Water). "I was really, really shocked. Especially when I saw pictures of the character, I was like, 'What? Aren't there a million other women walking around in Los Angeles right now who actually already look like this?'" Says Ziskin, "My joke is, I cast a blond as a famous redhead, and a redhead as a famous blond. There were a lot of hair issues."

Thomas Haden Church in Spider-Man 3.

Church, too, thought "Really?" when he got the call; after all, he had just reinvented himself as an indie star in Sideways. Though he hadn't been a fan of comic-book movies, he signed on because of Raimi. "I saw there's an acuity to Sam as a storyteller," he says.

Grace resembles Maguire and so was a more obvious choice to play a kind of doppelgänger to Spider-Man. And he was steeped in Spidey lore as a kid. "I remember I'd be reading comic books and my mom would say, 'Do your homework. Are you really going to use that when you grow up?' " he says. "I told you so, Mom." He admits that he was elated to be cast. "Watching Tobey in the first and second ones, I thought, 'Man, that must be the coolest job ever.'"

For his part, Maguire, 31, enjoyed going to the dark side in the third installment. "We had a lot of fun with that, Sam and I," he says. "The first days we were trying to figure out what the tone of that would be. We wanted it to be energized. We had to play with exactly where we could go to make a distinct character turn without it being totally out there."

Raimi was also intent on creating a greater sense of "vertigo" in the shooting of Spider-Man. "I wanted to get into his environment in this one and soar with him," he says.

"On the first one, they were still getting a handle on how to shoot the scenes of Spider-Man flying through the streets. The shots were more static," Franco says. "And now, Sam has been able to make it more dynamic by countering camera moves. As an audience member, you'll have more of an experience of being up there."