Dinas
is a bit like Snape. He thinks what he's doing is right - he's a little more evil than good - or is he?
Nobody
really knows just how bad to the bone Dinas is.
Lupin is currently under the Imperius Curse inflicted by the Minister of Magic. The Minister and Dinas are basically on the same side (although there is a little power struggle), and Dinas forgot to imperius Lupin, so the Minister had to do so himself - and a few of the staff to, to be sure.
Currently Dinas is seeking out Lupin to stop him, and Imperius him to his own will, not the Minister's. Because Dinas does not want to draw attention to somethign being wrong at the school - which would happen if 3 young students (the girls) ended up dead.