The Cottage Library on Sugar Loaf Lane by K.T. Dady

Gabe doesn’t want to return to Honeydale, but after his mum dies, someone has to sort her cottage. At least he gets to see his friend Allie again. There’s just one problem, she doesn’t seem happy to see him, and he has no idea why until he finds an old letter in amongst his mum’s belongings that changes both their lives forever.