They have a fair amount in common, I think. The main characters are about the same ages, and otherwise fairly similar. I don't want to delve too much and give anything away, but there are some plot similarities too.
The big difference between them, is the use of language. The Black Arrow takes place in medieval England and the dialogue is written in a quasi-archaic style that is off-putting to some people. If you can get past the dialogue though, and you liked Kidnapped, I think you would probably like this one too.
It was serialised by the BBC years ago, and for years afterwards Terry Wogan on the Breakfast show on Radio 2 would say "To horse, Peterkin!" at random - it was almost the catchphrase of the series!
The big difference between them, is the use of language. The Black Arrow takes place in medieval England and the dialogue is written in a quasi-archaic style that is off-putting to some people. If you can get past the dialogue though, and you liked Kidnapped, I think you would probably like this one too.