Maisie Hitchins lives in her grandmother's boarding house, longing for adventure. She idolizes the famous detective, Gilbert Carrington, and follows his every case. Together, with her faithful pup Eddie, Maisie is determined to follow even the slightest scent of a mystery - no matter what! Maisie can't help listening in when the famed star of the stage, Sarah Massey, visits a friend at the boarding house. Sarah is distraught - her beau, a mysterious young man, gave her a priceless emerald necklace, and it's now missing! Maisie is instantly intrigued, and decides to investigate the theatre. But nothing is what it seems in this world of make-believe.