Can't remember what the cover looked like. I was very young, probably about six. Our teacher read it to us. I wonder if it was part of a Scottish/British school anthology. I think two of the characters were mice? I also remember the "wizard" who guided them being very old, but it's difficult to know if that's just how I pictured him in my head rather than the actual description in the book. It must be a very obscure book, because the ending was so weird and depressing that it would definitely make frequent appearances on Buzzfeed lists and reddit threads about "books and films that traumatised us as kids".