Thanks. So do I. I did check the front door, and the weatherstripping is such that he should not be able to get out. If he doesn't turn up in a couple of days we'll put a wanted poster down at the front door, just in case.
This is the first Syrian hamster we've had and he's way more of a problem-solver than the Winter White/Campbells dwarf hamsters I've had over the years. For the dwarf hamsters you just leave a live-catch trap with a carrot in it for bait and it works every time - if they don't just walk up to you.
Thor was madly trying to get out of his cage last night, not sure what was up. He was clawing at every corner, hopping up and down, not sure what that was about. He toodled in his hamster ball for a while, madly, all over the place, but didn't want to come back out of it when we tried to put him back in his casa. Checked the cage, it's clean (more or less) and well-stocked. He appears to have scaled the frame on his wheel, and then slid the mesh that was covering the bin to one side - neat trick as it had some heavy books holding it down. (He's getting a regular barred cage when he is back from his bender!) He then would have fallen close to two feet to the floor - which worries me more. I thought I heard a squeak late last night, but then decided it was some noise from outside, probably. (Apparently not. I hope he's not injured.)
So, I'll be up all night until I find the Daughter's damned hamster. A goldfish woulda been easier.