A.J. Fikry, the grumpy owner of Island Books, is going through a hard time: his bookshop is failing, he has lost his beloved wife, and his prized possession - a rare first edition book has been stolen. Over time, he has given up on people, and even the books in his store, instead of offering solace, are yet another reminder of a world that is changing too rapidly.

But one day A.J. finds two-year-old Maya sitting on the bookshop floor, with a note attached to her asking the owner to look after her. His life - and Maya's - is changed forever.