Callie from Manchester loves to sing, but only when her father and two younger brothers are not at home. One day, she's singing, but then she hears the front door close shut. She's called downstairs where she meets Valeria, her father's new girlfriend. Callie is stunned when Dad announces that Valeria is going to be her stepmother, or 'bonus mum' as Valeria prefers. Callie isn't sure about this, so Dad sends her and Valeria away on a trip together so that they can get to know each other.