Clayton feels that he might need a few minutes to explain the situation to the apprentices, and wouldn't want to rush an introduction to Karlus, as the boy sounds like a decent sort and there's certainly no reason to be rude to him. For this reason, he's going to use Earth Glide to glide directly beneath the cage, but paying careful attention to the radius of his blindsense, which should allow him to detect an antimagic field as an opaque blank cutting into his awareness, which he's rather afraid of after the lich and which has the potential to really ruin his plan, so he's keeping his eyes are open for one, so to speak. (If he encounters such a thing, he'll immediately retreat to consider other options. I figure he'd be more wary of one than usual for the simple reason that their apprentices have not been able to escape.)
Once beneath the cage, he's going to use Wall Of Stone to completely enclose the wooden cage within a stone box that should rise suddenly from the ground on all sides and then clap shut overhead, with a few small slits in the roof for air just in case there's a delay, and only once the cage is enclosed and the apprentices shielded from prying eyes outside that Clayton will pop out of the ground in a relaxed lotus position right in the cage with the apprentices, and with a Light orison cast on a pebble in his hand just for their sake.
As the stone cube (rectangle? cone?) will be there until someone manages to break it down into rubble (doable, but probably not easy or quick) Clayton will have a calm chat with the apprentices first, just to make sure there's not more to the situation than he's aware of and that escape is indeed the best plan. If nothing too surprising is revealed that would change his mind, he should have enough time to prep them for the dive and shouldn't have to work too hard to convince them, with the possible exception of Karlus, unless their motivations are somewhat different than he'd expect due to new information or being drugged or some such. He's also going to take the opportunity to see if any of them seem in some way other than themselves, or acting suspicious, or, you know, anything other than generally traumatized.
If there are no hiccups (a very un-Clayton turn of events) and the apprentices don't say anything that make him think they shouldn't escape just yet, then whenever the denizens of Damning manage to break into this stone cube that has suddenly enveloped their captives, they should find a wooden cage with five figures slumped in it as if dead. Only upon actually getting a decent look would they notice that their captives have been transformed by some dark and powerful magic into scarecrows.
Perception: 1d20 + 15 ⇒ (2) + 15 = 17 (to see if anything "looks" different about the apprentices)
Sense Motive: 1d20 + 6 ⇒ (1) + 6 = 7 (to see if anything sounds different about the apprentices)
Diplomacy: 1d20 + 22 ⇒ (13) + 22 = 35 (to quickly convince them to tell him everything and to be cool about being spirited away through the ground)