Clever Little Thing by Helena Echlin
This psychological thriller is set in England. Charlotte, who is English, is married to Pete, an American. Pete works for a startup company using mushrooms to make biodegradable packaging. They have had some success, but are trying to get a big company on board, so Pete is working long hours. The couple have a daughter, Stella, who is eight, and Charlotte is pregnant with their second child.
Stella has a lot of the signs of being neurodivergent, but they've not had her tested. She is very sensitive to noise, likes her food separated, and taught herself to read early. She very interested in birds and science, and as we see at the beginning, on a trip to the beach, she finds a dead bird that she wants to bring home to examine. Some of her behaviours can be offputting for the neurotypical kids in her class, and Charlotte is trying to socialize her more.
Charlotte has a babysitter that looks after Stella, a woman named Blanka, who is very patient with her, and doesn't talk a lot. When Blanka suddenly quits without explanation, Charlotte is surprised and disappointed. When she finds out Blanka died a few days after quitting she is saddened. Shortly afterward, she begins to notice changes in Stella, who seems to be losing her fear over some things, but is becoming more withdrawn. She is using phrases that Blanka used to use like "Oh yes" in her responses, and doesn't seem interested in her usual passions. As Charlotte tries to make sense of these changes, Pete seems to think that Charlotte is making too much of it, and increasingly Charlotte feels herself alone, without anyone to tell her worries to. She reaches out to an unlikely ally and finds herself trusting to herself more than ever before.
This is a story that escalates slowly. We can see the changes in Stella as Charlotte notes them, and understand her growing worries, and why she takes some drastic actions. Charlotte loves Stella as she is, and while she wants Stella to be able to function more easily in school and have friends, she also feels that Stella isn't herself and finds herself thinking about Blanka and how Stella seems to be exhibiting more and more elements of Blanka's personality.
This is a story of manipulation, of love between mothers and daughters, with an eerie underlying tone. The touches of creepiness are so well done, and you feel Charlotte's frustration and desperation as she tries to understand and save her children.
Hard to put down.