The Last Present (Willow Falls, #4)

Amanda and Leo have a history with birthdays. Now their friend's little sister, Grace, has fallen into a strange frozen state on her birthday, and Amanda and Leo must travel in time in order to fix whatever's wrong. As they journey back to each of Grace's birthdays, they start seeing all sorts of patterns... which raise all sorts of questions.

Amanda and Leo are going to have to unravel the threads of the past and present - and travel much further than they ever imagined - if they're going to save Grace. Luckily, a little birthday magic always helps in the charming and funny Willow Falls series by Wendy Mass, where everything is possible and there are no coincidences.