"Dingus, Emily! If you ain't the one!"
I loved this book when I was a kid and must have borrowed it from our library ten times or more. I think it holds up fairly well, even if the ending is a bit unrealistic and rushed, and it's definitely one of those books that has stuck in my mind ever since reading it. Kipper is a particularly strong character, even if his figures of speech grow rather tiresome, and Emily is a likeable heroine (definitely reminiscent of Sarah in The Little Princess , though I didn't make that connection until reading other Goodreads reviews).
I may be reading too much into this, but I think the significance of the peppermints in the parlor (besides providing a catchy title) is that they represent what the majority of the characters--Aunt Twice, Emily, Tilly, and the old ones--can't have: a better life. They make snatches at it when stealing peppermints and, eventually, turn this symbol into a means of escape.
Overall, a fun read. I don't think I'd buy it, but I would recommend it, especially for young mystery fans.