In the mystery genre, “psychological suspense” is code for a book that readers can’t put down but in which little actually happens.

That’s not to imply that psychological suspense is boring. In the right hands, the tension mounts and readers keep turning pages hoping the characters they’ve come to care about don’t succumb to their darker sides. When violence occurs, it’s thrilling because something finally happens. But it’s also horrible and frightening and disappointing.

In “Half Broken Things” (Bantam, $22), Scottish writer Morag Joss has turned out a perfect example of a psychological suspense novel. She draws increasingly concentric circles around three lost characters who form a twisted sort of family and find happiness from which readers know no good will come.

Jean is a professional house sitter whose life is reflected in her depressing job: She has nothing that’s her own. She lives in others’ homes, following instructions (don’t use the living room, don’t light candles) while the owners are out of town.

She has lived by other people’s rules for years, but that changes this time. Perhaps it’s because she is 64 and the house-sitting company she works for is forcing her into retirement after this assignment. Jean believes the house speaks to her, and she uses that as a reason – not an excuse – for what happens. She breaks every rule. She starts wearing the owners’ clothes, raiding the wine cellar and even throwing out all the photographs of the owners’ family.

Jean places an ad, seeking information about a son she gave up for adoption more than 40 years earlier. It’s not clear this son ever existed, but Michael responds to the ad. He’s something of a two-bit con who has fallen on hard times.

At first sight, Michael knows Jean is not the mother who gave him up years ago – and Jean knows it, too. Before long, he moves in along with Steph, a pregnant teen he has fallen in love with.

The three form an unlikely but happy group in someone else’s beautiful manor, far enough from town to keep nosy neighbors at bay. Jean, whose chronology of events is interspersed with an omniscient narrator’s, explains it this way: “Not any one single thing, not one thing more than any of the others. It was all of us, and all of it: the way this place allowed each of us to stop struggling in our various ways, how it seemed to give us strength, how it seemed right to care for it so much, and for one another. All of it added up to more than just us.”

Things do happen. Steph has her baby, and the characters grow in ways they never thought possible, happy for the first time in their lives. But readers know it’s not to last – Joss reveals that very early on.

Joss’ characters are drawn so well, readers will find themselves forgiving what they do.

But at the same time, Joss gets repetitive. Perhaps it’s the structure she uses, in which the story is told, then we read about it again in Jean’s journal.

Britain’s Crime Writers Assn. gave “Half Broken Things” its award as best crime novel. It’s a heck of a book. But sometimes, less can be more.