Unfortunately, this is a time of sequels - not the easiest books to share. The Keys to the Kingdom is a series of 7 young adult fantasy books that start with Mister Monday and end with Lord Sunday (as you can see the books are titled after the days of the week). Young Arthur is approached by a strange man one afternoon as he is having an asthma attack during a PE run. Arthur is going to die and so has been selected as the Rightful Heir to the Architect. In true fantasy form, Arthur is transported to another dimension and has to fight the ruler's of the seven days to give back control of "the House" to the will of the Architect. The book is full of mystery and suspense as this young boy (who's about 12) is forced to give up everything to save the world he loves.
The book is reminiscent of A Wrinkle in Time and The Neverending Story - giving a new breath to an old genre. Knowing how it ends only encourages me to share this series. I will say the ending is not what I expected and not as happy as I would have pictured but it reminded me of the stories of my childhood.