Amos's mum has married the nice Mr Baldwin and calls him Henry. Amos doesn't know what he should call him, so he sticks with "Mr Baldwin" for a start.
Amos has loads of fun with him. Mr Baldwin has a talking budgie and the longest handkerchief in the world. He takes Amos to bed every night and tickles him until he's had enough or he thinks up funny stories with him. And he is always there when Amos needs help.
Amos therefore realises one day that Mr Baldwin is not just Mr Baldwin, but his dad, and indeed the best dad in the whole world!