Is grissom coming back to CSI?

Grissom (William Petersen) was supposed to be back for Catherine Willows' last episode as a regular in season 12, but producers decided against it. They didn't want it to overshadow her farewell. Both Grissom and Willows (Marg Helgenberger) returned for the two-hour final CSI episode "Immortality" on September 27, 2015, at the end of season 15.