S5·E8 Haunted

Jennifer Hill believes the spirit of her dead husband Alec, an Immortal, is still with her. She comes to Alec's old friend MacLeod and begs him to appease Alec's spirit by whacking the son-of-a-bitch who took Alec Hill's head. Richie finds himself strangely attracted to the grieving young widow -- until he realizes he's the son-of-a-bitch who took Alec Hill's head.