“Arthur’s Mantle” is episode eighteen of season nine of Stargate SG-1.
Sam is messing with a device found in the cave under Glastonbury Tor. She finally discovers something about it and Mitchell says ‘What have you got to lose?’ when Sam suggests trying something out. Famous last words.
They both appear to disappear, not that they realise it, then the device activates a display showing Ancient writing. When Dr Lee enters and he doesn’t see them, plus Sam walks through him, they realise something unexpected has happened. The latter especially being a bit of a give-away. Sam says that they may have gone out of phase and shifted to another dimension. And they can’t communicate with anyone else.
The Sodan, the free Jaffa who were first encountered in “Babylon”, send a message saying that they are under attack. One of their own has gone totally weird.
This looks to be the first time since “Avalon: Part 2” that Merlin and Arthur have been mentioned.
Okay, if you can’t pick things up because you’re out of phase, why don’t you fall through the floor? It’s made of the same type of stuff as the things you can’t pick up – matter. Mind you, you’d probably fall completely through the planet in that case. And how and what are they breathing?