Destroyers — Gwen Grant

When Primmy's father brings her a puppy, she is overjoyed, as she has wanted a dog for years. However, Primmy and her dog soon fall foul of Destiny Troy, who hates animals but especially dogs. Destiny and Dexter Troy own the Mill just up the lane from the house Primmy's parents rent. The Troys are Agents for the house, collecting rent and dealing directly with Primmy's parents. They are difficult people to deal with. There is a dark secret attached to the Troys. As chemists, they are engaged in chemical experiments in their Mill which no-one knows about, experiments which bring death in their wake. The disappearance not only of Primmy's puppy, Banjo, but also of her friend Jack's dog, Dusty, bring the two children and their friend, Sasha, into direct conflict with the Troys, whom by now Primmy is calling The Destroyers.
The explosive ending has Primmy being used as a guinea pig for the chemical experiment and all three children having to escape in order to stay alive. The question is, is it too late for Primmy? And is it too late for Dusty and Banjo?