Think real-life politics are hard to follow? Just try keeping track of the comings and goings of the CIA operatives that keep the revolving door spinning on CBS's sophomore series The Agency. Luckily, TV Guide Online wouldn't dream of letting you turn on the Sept. 28 season premiere without first updating your scorecards — and neither would the show's executive producer, '70s teen idol-turned-Joss Whedon wannabe Shaun Cassidy. Here, the former pop star reveals the changes in personnel — and direction — that he hopes will make sure the sleeper still rocks 'n' rolls for us.

Good-bye, Gil Bellows. "[It's] no reflection on Gil," says Cassidy of the Ally McBeal casualty who played Matt Callan. "Gil's terrific. But it's sort of like a basketball team. You have to kind of look at the whole and where do you need the strength and where do you need to beef things up. He did a very good job, but we needed somebody else more like this sort of character." Who's that, you say?

Hello, Jason O'Mara. Playing brawny A.B. Stiles among the brainiacs is the Irish hottie you probably saw in HBO's Band of Brothers. "He had a lot of faith in us," relates Cassidy, "because he really signed on based on a couple of conversations — the character didn't exist yet." Now that Stiles isn't just a gleam in the writer's eye, what can Cassidy tell us about the new guy? He'll be "a much more visceral character... than existed in the previous ensemble. We have very few people who serve more on action than words. That's what he's going to do."

See you soon, Gloria Reuben? The ER alumna may return to her recurring role of Lisa Fabrizzi. "It's possible she could come back in some capacity," Cassidy reveals. "But she's got a lot going on in her life and in her work. We'll see." In the meantime, Lolita Davidovich joins the cast as a special agent.

Welcome, Jennifer Garner. Okay, no, the Alias spy chick isn't coming aboard. But Cassidy muse Paige Turco (with whom he also worked on American Gothic) will get out from behind Terri Lowell's desk a lot more. "We love to see Paige kicking," jokes Cassidy, adding that it's not straining credulity to let a character like hers wield weapons that are deadlier than her computer keyboard. "Working in Officer Technical Services is where they began, but they are specifically trained to go out in the field and support case officers. You need to bug a room? You can't have [Stiles] doing that. You have people in OTS doing it."