Kyle Jennings was a murder suspect who was drugged with scopolamine by Tom Williams in such a way as to make him kill David Lock without having any memory of doing it. With Tom confident that the police would not be able to prove his conspiracy to commit murder, Kyle lent his zombie getup to Castle, so Tom would think that he's Kyle, looking for revenge, to scare a confession out of him. After Tom is arrested, Kyle tells Castle to keep his costume, deciding to leave the zombie subculture.