Monsieur Mustard curls his whiskers just so, slips on his fancy suit, looks at the handsome front-page picture on the newspaper announcing his arrival in the city of Bath, and chuckles happily to himself. As soon as he leaves the house, he is mobbed by admirers, as usual. But just as he starts to sniff out his first mystery, everything seems to go wrong: his detective bag is stolen, he is knocked off his feet and his monocle shatters. It appears that not everyone is happy to have a world-famous detective in their city . . . With the help of new friends, Mobbsy the flatulent shrew and Professor Thingummy the food-obsessed inventor, can Monsieur Mustard crack the case before the villain catches him?