Jenner
Jenner ran away a few years before Timothy got sick, so he is not there at the start of the book. He disagreed with the other rats' plan of living without stealing. Jenner disliked this and started to argue about the way of life they were living. They weren't ugly fights until Nicodemus decided to destroy the machines from The Toy Tinker. Jenner left the rat group with six others and walked away, maybe going back to NIMH. But in the begining, when they were captured in Chapter 14 to Chapter 22 they were great friends and still are, but not as great.