Spoilers Ahead:
I'm not going to lie, I didn't think I'd enjoy this book as much as I did. In a literary sense, it's not normally my type of book, but I actually think the concept was very interesting, and I'm intrigued about Lisa Stone as an author now.
We follow Jan as she's just been made redundant, and her boyfriend has broken up with her. She's needing a break, and someone places an advert for someone to look after their house and their dog for six months, whilst they're away working. The rent is low, and Jan needs to escape, so she accepts. So far, the house is alright, and she's enjoying the peace and quiet. After a bit of time, she realises that the house really isn't as peaceful as she thought. Tinder - excellent name for a dog, I might hasten to add - starts to growl in the evening, when it's dark. Originally, Jan thinks it must be an animal, and Tinder normally growls and chases after it. However, the tracks are unlike anything animal or human ever seen, and these start to get braver. They start to peer through the door, scaring her. Camille (who she's house-sitting for) has a friend called Chris, and they used to have a thing, but they broke it off, though Jan neve pried as to why. Chris calls in a lot of the time, but whenever Jan brings it up, he becomes defensive, and moody, and changes the subject. He disbelieves her sightings, and even though they go on one evening out, she doesn't think it will happen again.
Meanwhile, Ian and Emma are trying for their second baby. Their first baby ended in a TW miscarriage, and so they're worried. Very worried. As soon as the baby is born, Anne, their midwife, told them that their baby wasn't alive, and whisked it away without them seeing. She didn't want them to see the sight, and said it was better off for them. Later on, the police get a call from their neighbour, reporting a cry from the baby. Although there was no marked birth or death certificate, it wasn't deemed necessary, because it was a miscarriage before twenty-four weeks, and legally it's not necessary. The neighbour is adamant something is going on, but the police stop digging, as everything seems to be in order.
Back with Jan, these things are toying with her now, targeting her. It peers in through the doors, and although she tries to catch evidence of them, she never seems to be able to. Chris isn't believing a single word of what she says. When, one day, she catches evidence of them at the door, she shows Chris, and she knows he can't disregard her now, but he deletes the video. She now doesn't feel safe at all with him, knowing that he must somehow be involved. She swears she can hear a woman shouting for help behind her house, but, again, it's disproven. She's at her wits end, and then she begs Camille to come back, just so she can leave, as she doesn't want to be there anymore. Her friend, Ruby, comes down to stay with her, but leaves the next day, as it's also too much for her to take.
To get to the bottom of their TW miscarriage problem, Ian wants to do a DNA test, to see whether it's their genetics, and they can't have kids together. Emma is reluctant, because she wants to put everything behind them and mourn her baby, but Ian also wants to have a child with her. He does the DNA tests, and they come back that they're 99% compatible, meaning they have the exact same father. Upon looking into it further, he finds out that his wife, Emma, was created with a sperm donor, and that he, crazily enough, was also made with a sperm donor, from the exact same centre. He confronts the sperm donor company, but they offer him no insight into who his donor is, for confidentiality reasons. He is part an IT company, and so he hacks into the information, and finds out Anne, the midwife, is somehow linked into the situation, so he follows her. 
At night, he follows her into the woods in her van. Her neighbours said that she had dangerous dogs, and they had to be walked at night to avoid seeing anyone. He finds out she's not walking dogs; she's walking children. But not 'normal' children, children that look as if they have a primitive gene in them. He falls and is unconscious, and he wakes up at Anne's house. She tells him all about the children, about how they're all a product of incest. That the sperm donor company haven't been using donations, they've been using the owner's sperm for all couples. Anne looks after the children, although they don't have long to live most of the times. She keeps them happy and healthy for their short lives, and his son, David, is alive. Only for a few more months, though. These beings grow faster than 'normal', and so he was already growing rapidly, with a lot of fur on him. Ian decides not to tell Emma, as it would break her. They go separate ways, and Ian emails everyone affected by the sperm donor company, and the owner is finally arrested, and everyone can go back to their lives - as much as they possibly can. 
When Camille returns, the creatures return to the window, and she can no longer deny their existence to Jan. Camille tells them how her and Chris are actually related, and that's how they know the creatures, and that they won't hurt her. They lost their own child, and Jan is sad for them. Years later, her and Chris finally get together, and they're having a child of their own. In the scans, their child is known to have a club foot, which also happens to people that are immorally bred. He's scared, and he hopes that Jan and him aren't related. Jan has an email saying they are, but it's actually for her brother, and so they're not related, and their baby boy is born healthy. 
Well, I can say this book is heavy. To think it's based on a true case is actually wild. I thought the sinister side of things was very apt, and it kept me on my toes. I like the different POVs, and I like how both of their stories were intertwined. Honestly, there's not much I can say about this book. Even though there wasn't much humour in the book, I still devoured it in a day, and I can definitely say it's one of my faves. The only thing that was missing was the ending was a bit lacklustre for me. I, personally, despised Chris, and I don't think he had a worthy redemption arc to warrant marrying Jan. I think she could have done a whole lot better, and the ending was just a little rushed, for me. We already had a lot of plot twists, with Ian and Emma being related, and Chris and Camille, and the book could have ended a few chapters back, without the scare of Chris and Jan too. It didn't really add much for the story, and for that reason alone, I didn't give it five stars. However, it's a very, very good book, and I would definitely recommend.