S4, E20: The CSIs must find who is trying to kill a young, sexy couple just released from jail. Leo and Sienna's illegal activities transformed them from common criminals to media darlings, but now their past is catching up with them. However, after they are released from jail, their past misdeeds catch up with them. Meanwhile, Calleigh's ex-boyfriend from the U.S. Treasury office is assigned to help her on the case.