Episode406, "Day In The Life"
SEASON 4, EPISODE 411 - As Ed walks her up the aisle, Donnas wedding is violently interrupted by a vengeful family seeking to do harm to everyone close to her. She is shocked to learn that her former mentor, in an alcoholic haze, revealed the identity of the cops who brought old man Logan to justice, and sent him to prison. When Logan dies of stomach cancer, his widow starts a chain reaction campaign to kill people from her husbands captors families. That list includes Donnas fianc, who is shot twice at close range by her ex-mentor in the name of protecting Donna. The episode ends with him expected to survive.