1.) CHARACTERS. 
 I felt that there were shallow backgrounds on the characters. It all just skimmed the top, not delving into the deep backgrounds. It would have helped develop a sense of affinity and mystery on the characters and the story itself. As much as I feel this about the other characters, I really loved Elsa. Just the sheer fact that she loves Harry Potter made me love her. And don't get me started on how witty and smart she is. 
 2.) PLOT 
 The plot in itself is the reason why I picked up this book. It's such a mystery. Sending a seven-year-old to a mysterious puzzle? Uhm, yes please. It's excellent to be honest. But, let's just be realistic here for a moment. I was so stupid when I was seven years old. Well, more stupid than I am now. And I don't think, if this was in real life, that Elsa could have solved all the puzzles. 
 I really liked the book, but I was not lost in it. 
 3.) TITLE 
 I felt like the story didn't live up to the title. I mean, at first I thought there was a specified number of letters given to Elsa to give out to the people. And that SHE was the one to say sorry. Turned out she didn't even know the contents of the letters--even just the "sorry" part. And also at the cover, there's a dog. I thought it would help her somehow on her letter delivering. But I was wrong. 
 Obviously, I have some minor qualms about it. But I still liked it, nonetheless.