William Petersen, the patriarch of "CSI" who rode off into the sunset in 2009 presumably never to return to the grind of TV, is back in the grind: He's joined the cast of "Manhattan."

Say what? You've never heard of "Manhattan"? It's a good series on a less-than-prominent venue (WGN America) that will return for a second season later this year.

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Here's how WGN describes his character: "Petersen will play Colonel Emmett Darrow, the enigmatic new ranking military officer at Los Alamos, as a series regular for season two. A deeply religious and patriotic man, Darrow feels called by God to usher in the atomic future, and to spread American values across the globe."

As you have gleaned, "Manhattan" is not set in Manhattan, but is a period drama about the Manhattan Project. (Think "Mad Men" meets the atom bomb.) It also has a heck of a cast: John Benjamin Hickey, Olivia Williams, Daniel Stern, Ashley Zukerman and Rachel Brosnahan.