This is the portal fantasy with teeth you didn't know you were waiting for. Many authors have explored this territory, but very few have gotten the danger across without their books ending up intended for a grown-up audience, think 'The Magicians' and 'Wayward Children'.
Gewirtz has five siblings fall through their living room window after it mysteriously turns a deep blue and they end up in the world of Ganbihar. The rules are subtly different. The dangers of Ganbihar are its people. Language and intent and the people themselves are twisted, made somehow bestial by a great wrong of the past. The story's narrative is told in the third person and is passed in turns to each of the five children. It is a long journey for them, and the reader must share that, as they travel from the wilderness into a strange city and must flee to a sanctuary that isn't what it appears to be.
There is a message here, and I often have issues with books that that try to impart a lesson on a reader, but I feel Gewirtz handled the story well. The children's characters were distinct, the setting creepy, and the ideas underpinning the fabric of this world were fascinating. Echoes of Narnia are inevitable, but 'Blue Window' doesn't suffer from the comparison in my opinion. I'll be keeping an eye out for Gewirtz's next book.