With any Styx concert these days, there's a built-in element of suspense -- and it has nothing to do with the question of which of the Chicago-bred band's wide array of hits will be performed and which will not.
In fact, as keyboard man Lawrence Gowan tells it, the suspense isn't just out in the audience, it's onstage, too.
Call it the "Chuck Factor."
The Chuck Factor could have ramifications for Styx's return engagement Saturday to Bloomington's U.S. Cellular Coliseum, where the band appeared four years ago, alongside Foreigner.
The second time through the classic-rock vibe will continue apace, with Styx preceded by fellow '70s-'80s travelers Eddie Money and Loverboy.
The same configuration from Styx's 2007 Coliseum date remains intact: classic-era members James Young and Tommy Shaw, and post-classic recruits Todd Sucherman (since 1995), Gorman (since 1999) and Ricky Phillips (since 2003).
As has been the case for the past 15-odd years, the band's famous "wild card" remains founding member Chuck Panozzo, the bass player broadsided twice over the course of the band's epic, near-40-year run.
Panozzo lost his fraternal twin brother John, Styx's original drummer, to an early death (47) in 1996 -- on the eve, in fact, of a Peoria Civic Center concert.
Two years later, he was sidelined himself by his own HIV-related health problems.
As Shaw noted in a 2003 GO! interview, "Chuck's a free spirit now, and he's welcome back any time the spirit moves him."
Added Shaw: "He does still show up at times. It's a fun thing, and it's variety for us. The fans love to see him -- he's Styx royalty."
Eight years later, per Gowan's report, the Chuck Factor is still a part of that overall Styx experience -- now more than ever, perhaps.
"He's played more shows this year than he did last year," Gowan says. "Out of 100 dates, he's been there for probably a quarter of them."
Just days before the band's trek from California to the Midwest, Panozzo had turned up a string of recent West Coast dates.
"He had intended to show up for all of the nights, but he had a bit of a setback that precluded doing all of them," says Gowan.
And that's pretty much the regimen in the band's fourth decade: "It's always his intention to be there. It really comes down to the day itself -- if he's feeling up to it, he will."
The $64,000 question: Does Gowan think Panozzo will turn up on stage at the Coliseum come Saturday night?
"It's possible ... but he never makes that decision until the day of the show, and he'll usually show up to play around three songs on stage," says Gowan, the Scots-born, Canadian-reared singer-pianist who enjoyed his own notable solo career in Canada prior to being tagged as defecting member Dennis DeYoung's replacement in 1998.
"I'm so used to it, I just look over to stage left, and if I see movement, I know Chuck's there in the wings, ready to come out. And I do look -- every single night!"