Arthur's Mantle (episode)

Arthur's Mantle is the eighteenth episode of the ninth season of Stargate SG-1.

Plot
Col. Carter has been trying for weeks to find a way to access an Ancient device found in Merlin's cave in "Avalon", so far without success. Just as Col. Mitchell joins her to offer some breakfast, she manages to access the device, shifting them both into an alternate dimension. After their attempt to contact Daniel fails (they expected him to have the ability to see them, as he had experienced something very similar in a previous episode - "Crystal Skull"), they wait for the base personnel to detect them. Meanwhile, the SGC learns that the Sodan homeworld has been attacked and, as Mitchell is missing, Teal'c takes SG-12 to find out what happened.

On the base, Daniel finds out, by comparing security camera footage, that the device must be responsible for his colleagues' disappearance. At first Dr. Lee believes they have been miniaturised, but that theory is quickly abandoned. Daniel is reminded of the device that shifted him years ago, when he hears that this device emits lepton radiation, as well. He goes to study the manuscripts from Merlin's cave and discovers that Mitchell and Carter have been shifted much as he was. However, the device exists in both dimensions, so they begin to communicate by pressing buttons on the device.

Meanwhile on the Sodan homeworld, Teal'c learns that Volnek, a Jaffa nearly mortally wounded by Colonel Mitchell in an earlier episode, has been driven mad by a Prior and recently killed all villagers except for the chief, Haikon, who is badly wounded; he survives when a member of Teal'c's squad administers Tretonin treatment to compensate for the death of his symbiote (Volnek has, logically, struck at the traditional Jaffa weak spot when he was engaging the villagers). Haikon reveals that Volnek is using a cloaking device, and Teal'c decides to use one himself in order to find Volnek. He succeeds but is unable to kill him as Volnek simply rises to his feet when he is struck down by either staff blasts or Tau'ri weaponry.

In the meantime, General Landry sends SG-3 & SG-22 to support Teal'c's team when he does not report in; Mitchell, still invisible to the rest of the base, decides to tag along to help. Volnek, apparently retaining some measure of intelligence despite his madness, has disabled the device used by the Sodan to reach the Stargate from their lofty mountain village and has trapped Teal'c and SG-12 with him. Mitchell discovers that while Teal'c and Volnek are cloaked, they can see and hear him, but are unable to interact with him, effectively making Mitchell invincible against Volnek's enhanced strength. Mitchell and Teal'c decide to lure Volnek into an explosive trap, using claymores that will hopefully completely obliterate the body.

On Earth at the same time, Daniel has been shifted to the same dimension by a mistake of Dr. Lee and learns from the device's logs that Merlin used the device to hide his latest invention from his fellow Ascended Beings. Carter is shocked to learn that he willingly gave up Ascension, until she learns what he was hiding from the Others&mdash;a weapon capable of killing ascended beings. Daniel explains that Merlin believed that the Ori posed a threat to the people of the Milky Way, and anticipated the inaction of the Ancients. As far as Daniel can determine, Merlin completed the weapon, and Carter and Daniel learn that the weapon is on another planet, and the log contains the Stargate address.

Back in the regular dimension, Dr. Lee is further tinkering with the device and accidentally drains nearly all of its power. Daniel succeeds in bringing Carter and himself back just as they learn the coordinates where Merlin stored his prototype. Unfortunately, the device also affects Mitchell on the Sodan homeworld who had almost succeeded in luring Volnek into the trap. However, with some help from Teal'c, the trap succeeds after all and Volnek is reduced to minuscule and harmless pieces. Thankfully, Mitchell managed to remove the vital control crystal from Volnek's pocket before the explosive detonated and was able to repair the transport device.