Haven't They Grown – Sophie Hannah

Beth hasn't seen her best friend Flora for 12 years so she can't resist driving down Flora's street for a quick look at her house that he happens to be in the town.

She catches a glimpse of Flora herself, along with her two children Thomas and Emily who were five and three years old when they last met.

The problem is, Thomas and Emily still look five and three. And when makes Beth makes enquiries she discovers Flora, her tech billionaire husband and the children live in Florida.

Shocked, Beth embarks on an investigation that sees her more and more obsessed, alienating her husband, annoying a lot of people and even involving the police.

But despite all the setbacks she encounters, Beth is convinced something sinister is going on in Flora's apparently perfect family.

Haven't They Grown is a gripping stand-alone novel and a worthy successor to the excellent Did You See Melody, cementing Sophie Hannah's position as queen of the high-concept psychological mystery after she built a strong following with her twisty police procedurals and Hercule Poirot novels.

She can now offer up the most unlikely concept for a mystery novel and we'll go along for the ride, knowing it's worth our effort.

In Haven't They Grown, she presents us with an irresistible premise and wrings every possible twist and turn from its potential, as she takes us towards the inevitable climax.

But of course, the risks of setting up such an impossible mystery is that the final explanation will be either not worth waiting for, or too complicated for its own good. The latter, with credibility stretched to breaking point, is an occasional problem with Hannah's books.

But in this case, while her explanation flirts with unbelievability, it's presented with such page-turning energy, peril and confidence that we end up feeling satisfied rather than cheated.