Instaine - S8.E11

Sarah Spreadem had just found the perfect flat. Within walking distance of work, decent rent and a very nice landlord. But one day Sarah sees a large stain on the carpet that she was certain hadn’t been there before. When it resists scrubbing, she calls the landlord. However, no sooner has he walked in the door and the stain disappears! Just what is going on with Sarah’s underlay?