British author Clare Mackintosh exceeds high thriller expectations in THE LAST PARTY, a pulse-pounding investigation of the harsh effects of class and abuse that whips up an emotional storm of strong women and conflicting loyalties.

When a New Year's eve swimming event involving "everyone" from a small Welsh town results in the death of a local real estate developer, Detective Constable Ffion Morgan of the North Wales Police leaps into the investigation. But the death, soon likely to be called murder, took place in a lake that straddles the border between Wales and England, which means she'll have to work the case with Detective Constable Leo Brady of Cheshire Constabulary. And that's a huge problem: not so much because of the rivalry and resentments of that border area, but because the two DC's have met before ... for no-strings sex, both under assumed names. That's the trouble with online dating, isn't it?

But there's worse to come, because Ffion Morgan's small town is so very small that she knows almost everyone involved in the swim event, and as she and her unwanted partner begin to select suspects, some of them include people she know well ... very well. Family, even, whether by blood or by choice.

Mackintosh spins an expert high-risk investigation, with spicy inserts of lively humor. As the DCs struggle to place new names on each other, they're still spilling the earlier false names, to the confusion of the pathologist:

"Who the hell is Marcus?" the pathologist says. "I was told there were only the two of you coming—it's a morgue, not a séance."

"Sorry," Leo says on behalf of both of them, although Ffion doesn't look remotely sorry. Her expression is amused—a little quizzical—as though waiting for Leo to expand.

As Izzy Weaver ushers them into the depths of the mortuary, Leo feels a sense of misgiving come over him. He hopes to hell this turns out to be an accidental drowning, because Ffion Morgan looks like trouble.

The dead man is easily recognized as Rhys Lloyd, who owns the high-end resort on the English side of the lake and has made a fortune already in his maneuvers to bring in posh property owners. When Ffion and Leo split up the witness interviews, Leo finds Clemmie Northcote, an anomaly in the owners crowd: She and her son share a one-bedroom apartment in London where she sleeps on the couch, and she's financed her resort property through a private mortgage. "Although the others don't know I didn't buy it outright, so I'd be grateful if you'd keep that to yourself."

Leo's sympathy leads to Clemmie spilling more about the victim: "He looked down on us," she admits. "Me and Caleb. Because I don't wear the right clothes or drink the right wine. I didn't fit with his vision of The Shore." Leo notes the bitterness under her calm explanation. He hasn't yet said publicly that the death is actually murder, but Clemmie is already making a guess:

"If it were, I think you'd have your hands full."

"Why's that?"

Clemmie looks at him, her expression unguarded and resigned. "Because I've been at The Shore for six months, and I've yet to meet a single person who liked him."

Ffion too is finding disturbing currents in her part of the investigation. But the darkest of them are her own, and when the hunt for the murderer turns out to threaten her sister and even her mother, Ffion takes actions that she won't be able to admit to Leo, no matter how much she finds herself liking him. Envy and lust and abuse have flourished here—prying open the crime will reveal things that Ffion may not be able to withstand.

At a chunky 400 pages, this British crime novel takes time to unpack class, loyalty, and the desperate choices that desperate people make. Packed with a perfect balance of twists and layered revelation, it's a powerful novel well worth adding to the winter reading stack—and keeping on hand for later re-reading. Mackintosh already has five best-sellers under her belt (including last year's air highjacking drama HOSTAGE); THE LAST PARTY certainly deserves to be number six.

PS: Looking for more mystery reviews, from cozy to very dark? Browse the Kingdom Books mysteries review blog here.