Marty and her big sister Melissa couldn't be more different - and they just don't get along. Marty is a messy tomboy and loves animals, snuggling up in her cosy, comfy den, and drawing her comics - especially her favourite character, the brilliant Mighty Mart. So living with pink, girly, glittery, super-annoying Melissa has never been easy. But things are about to get much worse. When Mum's new dress-making business takes off, she needs a spare room in the house to use for her sewing. For the first time ever, Marty and Melissa have to share a room - and the girls are soon fighting every single day. But when one of their arguments leads to a serious accident, will Marty realise just how much her big sister really means to her?