The Rascal Cook (S01E09)

When a dead rat makes an unwelcome appearance on Hiverna restaurant's menu on their most important evening, head chef Len Tekler is beyond furious - someone is trying to stop him winning Arden Restaurant of the Year and he wants to know who. He calls in Frank and Lu, but they're unable to crack the case before the saboteur strikes again - causing a nasty bout of food poisoning leading to Hiverna's closure. (iTunes)