Karl is a parasitic worm: he spent a lot of time looking for his ideal habitat; he finally found it in a corner of the intestines where he can survive undisturbed... at least until today. Brian is a white blood cell: it is his first day of work; a faithful servant of the body but also a curious creature with a generous heart. He is supervised and directed by the omnipotent brain, that manifests itself in the appearance of a telephone.