Everybody Lies by Emily Cavanagh, Bookouture, 2020, 282 pages, $10.99.

Great Rock, the sea-island setting for Emily Cavanagh’s new novel Everybody Lies, is a close-knit place centered mainly on three towns — Osprey, Heron and Egret — whose population swells by many thousands during summer holiday season. It’s a place where “everyone is connected by three degrees of separation,” and where crowded summers and harsh winters create a small-town feeling that can call even its most prodigal natives back from great distances.

In other words, as a fictional stand-in for Martha’s Vineyard, it’ll do quite nicely.

It’s a place that works even on Ms. Cavanagh’s main character, middle-aged librarian Caroline Doherty, who reflects at one point in Everybody Lies about the odd, flinty beauty of this particular island.

“The purple sky at sunset on the beach, the ever-present smell of salt and fish in the air,” she thinks. “Somehow, without my even realizing it, Great Rock has seeped into my skin and taken root in my heart.”

But at the beginning of Everybody Lies, Caroline has plenty of reason to dislike the place. For 22 years, she was married to the Great Rock’s chief of police, Jack Doherty, and in that time she’s become bitterly aware of how pervasive the Doherty family is in island life. She and Jack have a grown young son, Connor, but in time since he’s moved out of their house for an apartment elsewhere on the island, Caroline’s become increasingly aware of the flaws in her marriage.

She and Jack are in a trial separation, which fills her with not only sadness but emotional confusion. “From a distance, I can love and miss Jack,” she reflects. “Up close, in real life, it’s not that simple. My love chafes and burns, too hot to touch, always leaving a mark.”

At the outset of Everybody Lies, when Jack comes over to the house they used to share, Caroline is expecting they’ll be having “the talk” about the future of their relationship. But instead, Jack delivers a stunning piece of news: a young woman named Layla has been found strangled to death on a nearby island beach.

The news is shocking to Caroline largely because of the nature of Great Rock itself, which she — and so many other people — view as a land from another time, “a place where people leave their doors unlocked and you know every neighbor on your street.”

Jack currently has no suspects, but, ominously, Layla was last seen at the bar where Connor works.

There opens from this upending start a multifaceted novel that Ms. Cavanagh tells from the perspectives of multiple characters. Jack’s suspicions quickly settle on their friend Ian, although it seems inconceivable to everybody that he could be involved.

“It’s unbelievable that anyone could think Ian had something to do with this,” Connor’s friend Daisy thinks. “Ian is a grounding force in our household, filling it with his loud laugh and the smells of his cooking.”

As the book’s byzantine plot-twists begin to mount, the book’s title increasingly comes into play, but there’s a good deal going on here aside from the main plot. Although the use of multiple perspectives can be distracting, Ms. Cavanagh has crafted an intensely thought-provoking look at the complexities that lurk underneath the sunny exteriors of vacation spots like Great Rock. As the darkness of the murder steadily spreads throughout the community, it uncovers many other darknesses hidden in the back rooms of local businesses and the bedrooms of local friends.

One of those darknesses grows more prominent as details about both Layla and local restaurant owners — and especially Connor — come to light is the sad fact that the opioid crisis currently wreaking havoc all over the country has not spared offshore places like Great Rock. 

Ms. Cavanagh adroitly peels away the layers of her characters — nobody escapes from this book unscathed — and this adds an appreciated psychological element to something that’s already an atmospheric murder mystery, and the appealingly human figure of Caroline Doherty grounds the whole thing. Readers of Everybody Lies will find themselves thinking about it the next time they take a vacation to a seemingly idyllic spot.