This is a very quick – one might say, too quick – read which throws up a number of interesting possibilities, but which ultimately fails to deliver on any of them. The story and characterisation are very weak and the spy plot is tissue-paper thin and unconvincing.

Sebastian Addison is the Earl of Claybrook, and has been the head of his family since he inherited his title at the age of sixteen. He’s also the government’s top spy and at the beginning of the book we meet him as he is parting from his latest lover, a widowed Italian contessa with whom he has just spent three glorious, sheet-burning days and nights of passion. They can never have anything more with each other, for the nature of his job means he can’t afford emotional entanglements.

Seven months later, he’s given a new assignment - to track down a man with known Jacobite sympathies who may represent a serious threat to the Crown. Imagine his surprise and shock when he is also presented with a partner who turns out to be none other than his passionate Italian contessa.

In case you couldn’t imagine it, I’ll tell you. He’s furious.

He scowls, gripes and sulks because a) he works alone and b) he’s annoyed that he was romping with a fellow operative back in Venice and had no idea Gabriella was in the same line of work (and thinks she must have known about him). Gabriella is more fatalistic about the whole thing, although rather hurt that Sebastian is trying so hard to get rid of her and doesn’t want her help.

Despite that, they still manage to have sex a couple of times, one of which is after she’s been shot. They’re not the only fictional couple to do this, of course, but I really can’t help wondering how she coped with the pain in the days before decent analgesia.

But I digress. When it comes down to it, the dangerous individual Sebastian and Gabrielle are trying to track down really couldn’t think his way out of a paper bag, let alone organise a rebellion, and I have no idea why the government was so worried about him. And the thrilling dénouement to the plot sees the crack lady-spy deliberately getting herself captured in order to distract the bad guys until the cavalry arrives to save the day. So much for the kick-arse heroine.

There is so much wasted potential in this book. The synopsis tells us : To society he is the Earl of Claybrook, the patriarch who raised his siblings after the death of their parents. But to the king, Sebastian is Britain’s top spy—a position that has taken an emotional toll on him. I was immediately put in mind of Vere in Sherry Thomas’ wonderful His at Night and was rubbing my hands with glee at the idea of a conflicted hero who has to conceal his secret “other life”. But sadly, there is no inner turmoil or depth to his character, and while Sebastian does stop to think “what’s it all for?” a couple of times, all we really see of that “emotional toll” is him throwing his toys out of the pram at being told to work with Gabrielle. There are a couple of throwaway lines in the book about how difficult he found it to adjust to being an earl and that he’s been a father figure to his siblings, but there’s nothing to explain how it came about that a man so concerned with looking after his family would be prepared to undertake dangerous missions and risk his life on a regular basis.

As a character, Gabrielle is more likeable and well-defined than Sebastian. She’s independent, intelligent and quick-witted - and able to look after herself in a fight. We learn that she’s not Italian and not a widowed contessa, but is a former street urchin who was rescued from the Covent Garden slums at the age of twelve and essentially brought up by the British government and turned into a weapon to be used as they saw fit. When Sebastian learns this, he is justifiably appalled, but when Gabriella explains to him that she is happy with the way things turned out, as otherwise she’d have ended up selling herself on the streets and probably facing an early death, he thinks she can’t possibly mean what she says and has another fit of the sulks at the idea that she’s had to sleep with men as part of her work – even though he’s done the same. (With women, of course.) There’s an interesting point here about the government training Gabrielle to prostitute herself in order to gain information which is glossed over; and her intelligent response is basically ignored in favour of Sebastian’s tantrum.

There’s no strong sense of time and place in the story. We’re told it’s six years after Culloden (1745) so it must be 1751, but in spite of brief mentions of Jacobites, powdered wigs and a coffee house, it could have taken place at almost any time in the 18th or 19th centuries. There are some glaring modernisms and Americanisms in the language, and the pacing is of the “blink-and-you-miss-it” variety, because almost nothing is allowed to settle or take root before moving on to the next thing, which makes the book feel utterly insubstantial. The only thing that’s ever dwelt on is the central couple’s continually lusting after each other and inwardly bemoaning how “dangerous” the other is to their peace of mind. Seriously? They shagged each other blind for 72 hours and then spent seven months apart, and I just wasn’t buying that there was any deep emotional connection between them.

One of the other things that made this book such a huge disappointment was that Ms Cullen’s last book – His Saving Grace - was so very good. Well written, strongly characterised and deeply emotional, I’d hoped for more of the same. Unfortunately, Sebastian’s Lady Spy doesn’t deliver any of those things.