Stepfather Christmas by Lapinski, L. D.

Written in an advent calendar structure (a chapter to read each day in December). 10-year-old Harper lives with her single mum and her older brother Will. All is happy and well, until Mum announces she is bringing her new boyfriend, Nick, home for the Christmas season. Nick is a bit – well – weird. He’s impossible to annoy, always jolly, an expert at fixing toys, has a white beard and works part-time on a reindeer farm – could he be Father Christmas? Harper certainly thinks so, no matter how much her brother tells her it’s nonsense – after all, after Nick arrives a reindeer shows up on the roof, a LOT of post suddenly starts coming for him, and snow falls but only seems to fill the family’s back garden! But when Nick starts spending unexplained time away from the family and keeping secrets, Harper and Will have to decide together if they really believe Nick is the big man himself.