William Petersen is planning a 'CSI' return to coincide with one very big exit.

According to TV Guide Magazine, Petersen will return to help longtime 'CSI' ster Marg Helgenberger exit the series.

"[Petersen] told me he's going to come back this season to help us with Marg's exit," series ster George Eads said.

Helgenberger is set to exit the series in January.

The last time Petersen made an appearance on 'CSI' was in surprise cameo in the Feb. 2011 episode 'The Two Mrs. Grissoms.'