Credit: Charisma Carpenter: Jean-Paul Aussenard/WireImage; Keith Carradine: Jemal Countess/WireImage; Matthew Davis: Jim Spellman/WireImage

It’s Tuesday afternoon at 4:46/EST, so that can only mean one thing: It’s time for another one of my dizzy-making casting roundups:

* Keith Carradine can’t seem to shake the FBI. Fresh off his stint as a G-man on Dexter, he’s been tapped to appear in three episodes of CBS’ Numb3rs as the Fed who stands in the way of Charlie (David Krumholtz) regaining his security clearance.

* Charisma Carpenter is rushing back to Greek, where she’ll reprise her role of Zeta Beta Zeta bigwig Tegan Walker. This time around, she faces off with another ZBZ VIP, My So-Called Life alum Senta Moses’ Lizzi, at the National Sorority Convention. Is it too early to reserve a ringside seat for the showdown?

* Finally, Matthew Davis (What About Brian) is joining the cast of Damages in a top-secret, recurring role. And by top-secret, I mean unknown-to-me.

Oh, and before I go, one little programming note: This week’s Ask Ausiello will not be going live on schedule at midnight. Due to the complexities of my press tour schedule, look for this week’s AA later on. Like maybe tomorrow afternoon. Or maybe tomorrow night. Or Thursday afternoon. What? Don’t you like surprises?