The Secret at St. Marys is based on the characters who live in a bayside suburb where everyday life is happy and fun. Cosmo is a lovable golden-haired Kelpie-Labrador who always wants to walk everywhere and experience new things. Bronte is a gray-and-white moggy cat that likes to visit her friend, Cosmo, whenever she can. She always looks for new things to do, and in this story, she finds out about a real secret that nobody is supposed to know. So she convinces Cosmo to help her find out what the secret is at St. Marys. Of course, they get into all sorts of trouble as they go from place to place and meet lots of different and interesting people.