I love me some animals. All kinds, from wild tigers to tame kitty cats. Lions and tigers and bears, oh my. Also parrots and penguins. The feistier they are, the better I like them. I try to put a pet as a character in each of my books because they are arguably an improvement over humans.
Spymaster’s Lady introduces us to Tiny, the huge black dog that guards the house. Annique calls him that "monster dog that stalks the halls, slavering and famished, seeking human flesh." She considers Tiny, not so much a dog, as "a wolf and possibly also part elephant." Annique is not one of the world's dog fanciers. But then, she spent her innocent girlhood sneaking into houses and stealing secrets. This gives one an ambivalent relationship with guard dogs.
Doyle found Tiny wandering by the London docks. "We think it's part wolfhound." Perhaps Tiny is the result of a mésalliance between an Irish wolfhound and a Newfoundland. They're both ancient breeds, becoming fairly widespread by the early Nineteenth Century. A cross between the two could plausibly have shown up in a cosmopolitan seaport like London. It would be one formidable dog.