the reason he was reluctant was because of what had happened at the plif christmas party , or , more accurately , because he could n't remember what had happened there , although rumour , started by big dave , had it that christopher had taken all his clothes off and insisted on going for a midnight swim in the river forth , during which activity he had had to be rescued from almost certain death by a couple of off-duty policemen wielding a life-belt and one of these long poles that lifeguards in swimming-pools sometimes have .