Tuesdays at the Castle is the first in Jessica Day George's Castle Glower series, which, although I suspect it's really meant to be for young adults, I totally liked. It's a fun series that still makes you think a little, and I love the ending to the book.
Tuesdays is on sale right now for $1.99 at Kindle and Kobo US, and discountable at Kobo. George's books don't go on sale very often, or for very long, so grab this one now if you want it! Just be warned that if you want to read the rest of the books in the series, the later titles go on sale even less often than this one...
Kindle US:
https://www.amazon.com/dp/B005PWMFQK
Kindle US/Smile:
https://smile.amazon.com/dp/B005PWMFQK
Kobo US:
https://www.kobo.com/us/en/ebook/tuesdays-at-the-castle