I think this might be MY favorite of the series ... perhaps because the characters have grown on me in time, but maybe, more likely because this book while still "middle grade" is skewed more toward the older audience? After all, here, Ivan becomes a DAD.  I felt like there were a few more heavy, note-worthy things here. With parenting, with dealing with the safe in captivity vs freedom in the wild thoughts.  That it's not a parent's most important job to protect their young from the world, but to prepare them for it. The author's note came out a little more forcefully on a few topics too. 

There were a few times when I really didn't know what was going to happen. While I didn't cry, I got a little more emotionally involved in this one. 

While Bob and Ruby make appearances, this one is Ivan's story again.