Twelve-year-old Mizzy dreams of being a detective and she won't let anything stand in her way — not her reputation for tall tales, or her embarrassing fear of escalators, and definitely not her Down syndrome. When she discovers Great Aunt Jane's diaries in a locked wardrobe in their spare room, and realizes her aunt didn't just die in her sleep but under suspicious circumstances, everything changes. Under the guise of a family tree project for school, and armed with a brand-new set of Pip-Squeaks markers, Mizzy grabs the chance to prove herself to her cousins — and the world.