The first brick was laid when he was four. From then on, with every year, course after course went up, though nobody, least of all Dean, knew it was happening. And by the time someone did notice, it was too late. The wall was up – with Dean - safe but alone – inside it.
It was Bobby that finally realised. He'd built his own wall after all – so he knew the signs. The funny thing was, it was Dean and Sam that had helped him build a doorway in his own wall. Maybe, eventually, he could return the favour to Dean.