Siobhan was Slim for Life's 'Slimmer of the Year' which makes her the ideal leader of the local club.  Unfortunately, her unwarranted feeling of superiority means her autocratic rule is achieved through shaming and condescension.  She expects religious devotion to the cause and her remaining disciples are willing participants.  When new members join the group, it becomes clear that they're not prepared for this level of devotion; and Siobhan's theology, and mind, begin to unravel.  It's the triumph over discipline and sacrifice that every woman wants to see!  Let's hear it for the girls... and biscuits!