Mum is clearing out the house and orders Dennis to pack up some old junk and then clean his room. During the cleaning, Dennis comes across a bundle of objects that inspire him to be a private investigator. Gran comes round to see if she can find one of her old teapots as she needs it for a date with a gentleman later on that day, so Dennis takes up the missing teapot as his first case. Starting off their trail by searching the town for the teapot, Dennis and Gnasher go back to the crime scene to investigate, and just as Gran has given up hope of finding the teapot in time for her date, Dennis sees Dad with the teapot. Gran rushes towards it and drops it. Dennis is devastated that it is smashed, but Gran reveals that it was what was inside the teapot that mattered most—her extra special set of diamond encrusted false teeth, found just in time for the arrival of her date.