Hi,
I mean it is in the past.
Can I say? The new gladiator would have been a fool if he had thought he was following the moral code where his world respected.
This is fine: The new gladiator would have been a fool if he had thought he was following the moral code which his world respected.
'Where' doesn't work here. Don't worry, I don't mind telling you again, it's no trouble for me. The main thing is that you need to understand.
The simple past would often be used here instead of the past perfect.
I mean " the three people over there in the corner". Then you can be specific, say 'killing the others'.
Best wishes yet again, Clive