3x11 - Forever Knight

A routine investigation into a suicide leads Nick and Tracy to an exorcist. As they witness an exorcism, Nick is overpowered by a terrible evil. Unable to control himself, Nick turns to LaCroix for help. But even LaCroix is powerless in the face of this evil, and at Nicks request, takes him to the exorcist to help free him from the Son of Belial.