Day and Night and the Ritual

Night found humans when he escaped some Military compound. He hides as a cat. When he thought that nothing bad would happen, he was kidnapped! Cat-napped? Dragon-napped? Well, whatever it would be called. Where he ended up, he was reunited with his sister Day! Day was hidden as an Australian Sheppard. Soon they find out why they were taken! Wilhelm the head of the agency or whatever it's called, took them so they could perform a ritual to release an ancient evil! Can they stop the ritual?