Leo was a killer hired by an unknown individual (later revealed to be fellow Secret Service Agent Jim) to murder Sam Martino, Myka's old partner in the Secret Service. He came into contact with an artifact that could freeze time. During a mission Pete and Myka were on, they saw him and Myka recognized Leo as the man who killed Sam. Both of them failed to capture him, and Myka and Pete had to work with two of her former colleagues, Zach and Jim, to capture Leo. Myka spotted him again and this time she and Pete gave chase. Leo however used the artifact to escape. This aroused the agents' suspicions, and they gradually pieced together what must have happened. They cornered Leo, but Jim activated the artifact and, during the time-freeze, placed a gun in Leo's hand, then, when time flowed again, shot Leo, citing self-defense. Myka, however, noticed Leo's confusion before he was shot, along with the fact that the gun was in his right hand, although Leo was a leftie. This led to the conclusion that he was framed, and, eventually, to the retrieval of the barometer after Jim was accidentally shot by Zach.