The Fifth Man (S05E04)

While under fire on an alien world, Carter, Daniel and Teal'c return through the Stargate and report to General Hammond that Col. O'Neill stayed behind to protect the wounded Lt. Tyler. Hammond is confused, asking "who is Lt. Tyler?" Carter says that Tyler is the new member of SG-1, has been for the past month, and that this is actually his third mission with them. Hammond informs the team that there is not, nor has there ever been a fifth member of SG-1 named Tyler and orders them to the infirmary to be examined. While Dr. Fraiser can't find anything physically wrong with them, they continue to insist that Tyler is real and that reinforcements must be sent immediately to rescue him and O'Neill. Hammond believes that SG-1 has fallen victim to some alien technology and makes the decision to quarantine them while he gets to the bottom of the mystery. Back on the planet, O'Neill and the badly wounded Tyler must battle for their lives, O'Neill acting as a vitual one-man army against the numerous encroaching Jaffa. But at SGC, the Pentagon's Col. Simmons has gotten word that SG-1 has been compromised and he uses the situation to try and destroy their credibility as well as expose the threats that he believes the Stargate Program poses to national security. Carter, Daniel, Teal'c and Dr. Fraiser struggle to unravel the mystery in order to save Col. O'Neill as well as the future of Stargate Command. (Metro-Goldwyn-Mayer (MGM))