At first, Hank Phillippi Ryan’s “Mother Daughter Sister Stranger” seems pretty straightforward. In fact, after the first few chapters, I was wondering how she would make this really suspenseful when it’s about a woman who is taking care of her 11-year-old niece for a week while her sister is on vacation. And her sister doesn’t show up on the day she was supposed to.

But once the action starts, it’s pretty much nonstop. I found myself racing through the last three-quarters of the book to find out what was going on. And while I was able to figure out some of it, most was well hidden in the morass of guilty people, long-held secrets, family betrayals, deaths, and even a serial killer. This is not a novel for readers with delicate sensibilities.

Eliza and Bea Ramsey were used to relying on each other after their parents were killed in a small plane crash that almost killed the two girls. They recovered under the care of their Aunt Margaret, and while Eliza would like to be close to Bea, Bea’s lifestyle and choice of partner have made that difficult. But one thing that they are united on, without fail, is the Ramsey Remembrance Day which they “celebrate,” or remember, on the yearly anniversary of their parents’ death — the date that changed their lives and tore them from their loving parents.

Both girls have successful lives. Eliza is a book agent specializing in romance novels because she loves happy endings. Bea has become a fashion influencer and has closets overflowing with expensive couture. Bea hasn’t been as open with Eliza since she married Kyle, ten years her elder and very bossy. So when Bea presented Eliza with Piper, the five-year-old daughter she and Kyle had just adopted, Eliza was blindsided and disappointed, but not shocked that Bea hadn’t shared anything leading up to the adoption. She also hasn’t shared much about her recent divorce from Kyle.

At the beginning of the novel, we see that Bea doesn’t arrive to pick up Piper as agreed. Piper is worried, and keeps checking out the window. To distract her, Eliza asks Piper, “What’s the happiest ending you can imagine?” because that’s how Eliza views life — she wants to see the happy endings. She even imagines what happens in books with not-happy endings after the last page. How can a sad ending be turned around? Piper thinks pizza sounds like a happy ending, and it helps. At that moment.

But as the days pass and Bea doesn’t show up or answer her phone or respond to texts, Eliza and Piper are very worried. And because Eliza is the adult, she has to reassure Piper that everything will be okay. They go to Piper’s house and Eliza sees that all the clothes in Bea’s huge closet have disappeared. Has Bea intentionally disappeared? Been kidnapped? Killed?

There’s much history that is shared about the Ramsey family, and the girls’ very successful parents: a father who was a professor and a mother who was a lawyer and judge. Their dad was a pilot and they flew to the Berkshires in their small private plane. They spent summers in the Berkshires where, we learn, a serial killer had haunted the girls’ teenage years. During the summer at their vacation home, girls had been murdered. Their parents didn’t let the girls be outside after dark, and everyone wondered who the murderer, known as the Greylock Killer, was.

There’s also Whitney, Eliza’s boss and head of the literary agency. She’s become very involved in helping Eliza with Piper now that Bea is missing. It’s helpful, but also very suspicious. Whitney and Eliza had never been close. Why does Whitney seem so interested in Piper and Bea? When Eliza finds a manuscript about the Greylock killer, more questions arise.

Ryan’s masterful use of Eliza’s first person narrative ratchets up the tension as we feel her fear when mysterious notes appear, a shadowy figure moves the curtains in her apartment as she and Piper watch from below, and she doesn’t know where to turn and where is safe. Finally, she and Piper flee to the summer home in the Berkshires, where the story comes full circle, and all her questions will be answered.

This is truly a story that will truly keep you up late at night in your rush to find out the resolution. And while you might guess some of it, I’m predicting few readers will be able to figure out the entirety of this cleverly plotted, thrilling mystery.

This review was first posted on Bookreporter.com.