As is so often the case with science fiction, we aren't exactly sure what's going on in ABC's new series "Invasion."

Something is out there — as they say — but we don't exactly know what.

For that matter, we don't even really know what the title of the show, airing tonight at 9 p.m. on Ch. 4, means. Sure, it could mean that Earth is being invaded by aliens — which is what seems to be happening — but it could mean other things, too. Who or what is invading?

"Who's 'The Godfather'?" creator/executive producer Shaun Cassidy asked in cryptic response. "Is it Michael or is it Vito?"

"The invasion is the hurricane" that kicked off the series, said Cassidy. "The invasion is the new stepfather in the home. The invasion is the baby in my body. The invasion is the orange things in the water. The invasion is change and how we acclimate and how we respond and how we survive against pretty formidable odds. I know that's broad and highfalutin' — blah, blah, blah, blah — but that's sort of what it is.

"Our show is about a dad trying to protect his family, about a sheriff trying to protect his family in his greater community against a threat. You don't need an alien. A hurricane can be pretty devastating. Divorce can be pretty devastating. It's all subjective."

Since his days as a wholesome teen idol (starring in "The Hardy Boys Mysteries" and singing "Da Do Ron Ron"), Cassidy has sort of turned to the dark side as a writer and producer. In addition to "Invasion," the TV shows he has created and produced include "Roar" and "American Gothic" (in addition to less offbeat efforts such as "The Mountain," "Cold Case" and "The Agency").

Where does his dark side come from?

"I'm Irish," Cassidy joked. "I have a dark sense of humor. There's a lot of humor in this show.

"Darkness and light, it's all about the balance. Trying to solve the problems of the world in a little community in the aftermath of a hurricane or, in the case of a blended family — in the aftermath of divorce and remarriage — it's all the tools you need. There is darkness there, but there is great light. And, frankly, hope and optimism is what drives me. It's what's driving the show."

Where it's driving the show . . . well, we're just going to have to wait to find out.

SHOOTING THOSE hurricane scenes in the pilot wasn't easy.

"It was hard to breathe because there was this big, like, fan machine," said 8-year-old Ariel Gade, who plays Rose in the show. "I couldn't breathe, because it was blowing so hard."

"We suffocated all the children on the show," deadpanned Tyler Labine, the 27-year-old who plays Dave.

AS IS ALSO OFTEN the case, the people who watch a sci-fi show seem to take it more seriously than the people who are starring in it. As evidenced by a highfalutin' question asked about whether actors playing the younger characters in "Invasion" think they are going to rise to the occasion in the aftermath of the hurricane and show great strength of character.

"Um, no," said 18-year-old Evan Peters, who plays Jesse. "I don't know. I just want to get a gun and shoot aliens."

Good answer.

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E-mail: pierce@desnews.com