A Central Theme of “Belly Up” by Stuart Gibbs is that if no one else steps up, you have to do it yourself, even if someone tries to stop you. In the last few pages of chapter 4, after his call with the police talking about Henry's death and being called a prank caller, he says, “I was going to have to investigate Henry's murder myself.” If the police wouldn't even help him, then he would have to help himself. Also, in chapter 9, after someone tried to kill him with a black mamba, they also opened its exhibit. He and his mom said, “Are you saying someone tried to hurt you?” “I think so.” If someone tried to hurt him for investigating, then that means Someone is probably trying to scare Teddy off. A central theme in Belly Up by Stuart Gibbs is that if no one else steps up, you have to do it yourself, even if someone tries to stop you.