Mother Island by Bethan Roberts, book review: Tale of jealous mind makes for gripping thriller

There's little more engrossing than a top-notch psychological thriller. Bethan Roberts's latest novel doesn't disappoint – it's satisfyingly creepy and stimulates that delicious paradox: goose-pimples in summer.

The novel starts in the present. Maggie, a nanny and loner, is planning with matter-of-fact calm how she will steal the baby she is employed to look after, Samuel. Samuel belongs to Maggie's cousin Nula and Nula's cocky husband Greg. There are chilling glimpses that a deep resentment has been festering in Maggie for a long time: "It had been 16 years. Maggie had counted every one."

The action shifts to various times in the past, and we gain insights into Nula's postpartum depression, Maggie's life, and, most compellingly, a summer that Nula spent with Maggie's family on Anglesey, during which relationships were forged and broken.

The chapters are in the third-person, but seen from the perspective of either Maggie or Nula. Interspersed with these are shifts back to the present, and Maggie's abduction of Samuel.

Roberts is excellent on Maggie's distorted view; her deluded belief that Samuel belongs with her. When Samuel buries his head in his mother's lap as Maggie leaves after a routine day, Maggie misinterprets the gesture as showing that he can't bear to say goodbye to her. When he turns his face away from Maggie one Saturday, she tickles him and tells Nula that they have a private joke. She is convinced that she knows best as far as care of Samuel is concerned, even though she feeds him chocolate, and reheats rice and chicken several times.

Roberts is also good on the way mothers feel threatened by the closeness their babies develop to others. In fact, one of the themes of the novel is jealousy: that of a mother for her baby's affection for his nanny; that of a sister for her brother's infatuation with a girlfriend; that of a girl for the attention bestowed by her father onto her aunt or cousin.

There are a couple of times when Roberts's use of tense seems slightly off: a momentary shift from the perfect past tense to the present tense on page 22, and, in a scene on page 134 set in the past in which the action shifts briefly to the more distant past. But these are tiny gripes. The writing is simple and accessible but proficient, engaging and quietly convincing, with occasional inspired sentences, such as the description of the faces of a harried mother and screaming toddler as "pink explosions of fury".

It is not as dazzlingly perceptive of every detail as my thriller chiller of the year, Harriet Lane's Her, but it certainly comes close.