I have written the merest summary of it in the link under my blog heading, but * here is a better one that may give you a clearer idea of how profound, unsettling and interesting it is.
My battered early copy of The Mouse and His Child with its illustrations by Lillian Hoban, would be one of the first things I would try and grab if I ever actually succeed in setting my house on fire by walking away when I had put the tea on.
Incidentally I'm very impressed that Jenny Brown and her friend Teresa at Shelf Love have posted a list of books they have read in the last twenty years. Their blog of reviews began about ten years ago, and that's a long-running blog too.
*If the first link doesn't work, here it is again: https://shelflove.wordpress.com/2012/08/09/the-mouse-and-his-child-review.
If you want another personal reaction to the book, there's one by Stuart Kelly of the Guardian, here.
If you want a review with more of the plot explained (spoilers alert), you can also find one here at Tygertale.
Just to complete this little round-up, there is now a wiki page for the book here, and the animated film version here.
Finally, if you are thinking to purchase this for a child, I would mention that both the book and the animated movie have parts that are rather scary, even 'nightmarish' for some children, although this book certainly sits somewhere in the children's book genre. Perhaps a perfect one to read to them, and then discuss the meaning and metaphysics afterwards.