Marine Sgt. Todd Sommer, 23, seemed to be in peak physical condition before he suddenly collapsed and died in February of 2002. The official cause of death was listed as cardiac arrhythmia, but to one NCIS agent, something about the case seemed a little too familiar. In January of 2007, Cynthia Sommer was convicted of Todd's murder. But did she actually poison her husband, or was she being judged for her scandalous behavior? Usually a verdict means the end of a case, but for Cynthia Sommer, the biggest surprise was yet to come. Correspondent Richard Schlesinger reports the dramatic new developments on 48 HOURS MYSTERY: "An Invisible Enemy". Updated from and episode that aired on 2007-12-08.