Back at Stargate Command on earth, General Landry receives a scary piece of Intel: the Trust has been infiltrated by the SC’s old enemy the Goa’uld. Fearing an incursion from the Wraith, the Goa’uld have decided to rid themselves of these new meddlesome rivals by destroying Atlantis with a bomb. The reasoning is that with Atlantis gone, the Wraith will never find earth and become a threat to the Goa’uld. The bomb is set to go off the next time Atlantis contacts Stargate Command, which will be within a matter of hours, when Atlantis is due to make its weekly contact with earth. Landry is faced with a quandary: if he tries to contact Atlantis in order to warn them, that very communiqué will set off the bomb. And time is running out before Atlantis unwittingly blows themselves up by contacting earth.

Critical Mass works so well on many levels--one being the fact that the actual threat that’s laid out at first is unexpectantly thwarted within the opening ten minutes. And yet the tension unrepentantly continues, as the Atlantis team frantically works to not only find the still-live bomb, but also discover who planted it in the first place. This search for the bomber leads Weir into a nightmarish quagmire of an investigation where she must suspect everyone on Atlantis, as well as the crew of the Daedalus. Another aspect of Critical Mass that works so well is how it uses the large cast so effectively, including the talented bit players--such as Lt. Laura Cadman (Jaime Ray Newman), Dr. Lindsey Novak (Ellie Harvie) and Dr. Kavanagh (Ben Cotton)--who all find themselves being under suspicion as possible suspects.

The tension-filled race against time is augmented by the mystery of who the bomber might be--not to mention the taunt drama that’s created when Weir is forced to order harsher interrogation procedures (in other words, torture) on one particular prime suspect. Even the ’B’ story, with Teyla dealing with the potential loss of a beloved mentor, dove-tails nicely into the larger story. Although Teyla’s insistence at performing a sacred ceremony right in the midst of this crisis doesn’t ring true, the song she sings is efficiently used in the final, nail-biting climatic scenes. But Critical Mass is more than just a suspenseful episode; it’s a fine example of successfully using all of its characters in such a way that each of them has a moment to shine--as well as how, in the second season, Stargate: Atlantis itself began to gel into an entertaining series in its own right.