When a man covered in blood thinks he killed someone but has no memory of how he got blood on him, Horatio and the team have the tough job of filling in his memory. The man, Doug Benson, has amnesia brought on by a traumatic event. Unsure if he is the killer, the team processes him and with each new clue, it triggers a memory. Blood evidence on his clothes reveals a father, mother and daughter have been murdered. As hazy memories start to return, the CSIs find the dead family as well as the murder weapon with Doug's prints on it. It appears Doug is indeed the killer, until evidence at the murder scene proves the presence of another person and that Doug was forced at gunpoint to kill people he didn't even know. Also, Delko takes a personal interest in the case after having his own bout with amnesia following the shooting.