Shaun Cassidy likes a little mystery in his life. He was a Hardy Boy, after all. Plus, there was that baffling business with the ''Da Doo Ron Ron.'' More recently, in his second life as a TV producer, Cassidy created the creepy 1995 soap American Gothic and ran CBS' 2001 CIA spook show The Agency both short-lived. Now there's ABC's Invasion, an enigmatic serial starring Eddie Cibrian (Third Watch) and William Fichtner (The Longest Yard) about a Florida town recovering from a hurricane that brought with it a big wave of weirdness (and some glowing orange orbs, to boot). Alien incursion? Mass demonic possession? Old folks gone loco? Whatever it is, the timing of Cassidy's idea could not have been more perfect. ''I had the fortuitous luck of pitching this show the day after Lost premiered,'' says Cassidy. ''The gods were smiling on me that day.''
And on a few others, as well. The geeked-up crypto-drama is the season's most conspicuous programming trend, with CBS' Threshold (aliens!), The WB's Supernatural (boogeymen!), and NBC's Surface (sea monsters!). Given that Invasion is nestled behind J.J. Abrams' bewildering isle on Wednesday nights, it may stand the best chance of scaring up viewers. ''Lost has sparked a rush of 'big idea' shows,'' says Steve McPherson, president of ABC Entertainment. ''We felt Invasion could be compatible with Lost, but we didn't want it to be another Lost.''
That sounds like the usual ''This show's different'' spin, but the point is valid with Invasion. For all its otherworldly lights in the sky and mutant skeletons in the swamp, Invasion twists and turns on familiar underpinnings: It's about a divorced couple (Cibrian and Kari Matchett) settling in with new spouses (FreakyLink's Lisa Sheridan and Fichtner, respectively), and dealing with all the emotional awkwardness that can mean for their kids. ''That's what interested me,'' says Fichtner, whose shady Sheriff Underlay knows more about the hellacious hurricane than he's telling. ''I didn't want to chase no six-tooth monster.'' Adds Cibrian, who plays forest ranger Russell, Invasion's Scullyish voice of reason, ''There are bits of mystery and sci-fi, but there's a very strong family dynamic.''
That's not a coincidence. ''I'm interested in complicated families. I come from one,'' says Cassidy, 46, son of The Partridge Family's Shirley Jones, half brother to David Cassidy, and thrice-married father of four. Invasion, he continues, is what you get when your new wife from Homestead, Fla., tells you stories about surviving Hurricane Andrew which then mingle with your notions of making a Rosemary's Baby-type thriller. ''Invasion is an allegory,'' says Cassidy. ''This little town is a microcosm for how you deal with your life and with the unknown post-disaster.''
Invasion may have many meanings for Cassidy, but he agrees that most people are going to assume that it's all about little green men. The pilot doesn't discourage this thinking: Russell's brother-in-law (Tyler Labine) is an ET-believing conspiracy theorist, while characters go missing and come back...changed. Still, Cassidy says that as the conflict between Underlay and Russell escalates from personal to ideological to perhaps political, the little-green-men question will become more gray. Or it may not. ''I ran a show about the CIA,'' says Cassidy. ''I cannot confirm or deny anything.''