Critical Mass

S2 E13: General Landry (Beau Bridges) informs the team that the Goa'uld have planted a bomb on Atlantis and will be triggered by any attempt to dial the gate. After some investigation McKay (David Hewlett) determines that the failsafe mechanism on Atlantis' energy source hase been disabled -- so any action that might cause it to overload (such as dialing the gate) would result in an explosion. Furthermore the mechanism is now locked with an unbreakable code and they must find the individual who tampered with it in order to enable it once again. To make matters worse two Wraith cruisers are headed straight for Atlantis. They must activate the cloak in order to keep the city invisible to the Wraith - but such an operation would surely cause the energy source to detonate. With time running out an alarmed Weir (Torri Higginson) launches a full-scale investigation to find the saoteur. She is shocked when she discovers that the perpetrator is a member of her own team.