Its a great but just one thing
Savannah and Darren get more annoying as the story goes.
Savannah, could've just left with Cleo, and it would've made a good book that alone but she was dumb enough to rescue the other animals. Sure, this was a kind choice, but not a smart one. This led all sorts of problems for the other characters. She had to think about the consequences and her friends, not just her love for animals. Also, I think she has a sense of brag. Even though she did confess that it was her fault later on, she is still kind of annoying.
Darren on the other hand, isn't as annoying. Sure, in Swindle, I didn't like him too much. He isn't as bad in Zoobreak. In fact I kind of felt sorry for him. Sure, he had his problems. He didn't show up for the zoobreak, bulied Griffin, and used the animals for money. But being accused for a crime that he didn't do, having nigtmares about his trial.
Overall I give it a 74%. OK