Set partly in the late eighteen seventies and partly in the early nineteen twenties, The Shadow Hour is the story of two governesses, grandmother Harriet and grand-daughter Grace, whose lives become inextricably bound up with those of the family whose children they are engaged to teach.

The plot is complex and, frankly, rather contrived, being dependent on coincidences and on an inherited gift of clairvoyance that Harriet and Grace refer to as the 'glimmers'. Moreover, it takes a long time to unfold and I grew impatient, feeling the pacing could have been better managed.

What gives the book its strength, however, is the atmospheric quality of Riordan's writing. She is particularly good at period detail and at telling sense-impressions. I loved this description of a railway carriage:

Taking a seat in first class, he breathed in the familiar scent of a carriage on a fine spring morning. They smelt different according to the weather and season. Warmed dust, shaving soap and a hint of varnish on dry days; mackintosh wax and damp wool on wet ones. Winter after a downpour was least pleasant, stale smoke and sour breath turning the tightly closed windows opaque.

Readers who enjoy recycling the tropes of governess fiction - an old house, ageing servants, family secrets and and plucky but dis-empowered heroine - will love this. Others must content themselves with the very considerable flashes of talent in those descriptive passages.