It seems young Sheltie had spent the night pushing the tube that leads to his external wheel out of the cage, then escaped through the hole. Luckily he hadn't gone far: rather than hiding under the heaviest available piece of furniture like any sensible rodent, he was hanging about behind the TV table where the gerbil cages and accessories are housed.
As we pursued him he regarded us with curiosity, wandering up to us in a tantalising fashion as if wondering what all the fuss was about. I did manage to grab him, but he executed a vertical leap with aerial three-point turn out of my hands and shot off again. Eventually calgor trapped him in a box and I sort of poured him back into his cage.
I arrived at the office feeling as though I'd done a week's work already.