For a group of ex-RAF comrades, it is to be the reunion to end all reunions: a weekend in the Scottish castle where they were guinea pigs in a psychological experiment many years before. Most of them haven’t seen each other since. But the convivial atmosphere on the journey north is quickly shattered by the apparent suicide of one of their party.

When a second death occurs, a sense of foreboding descends on the group. It appears that the past is coming back to haunt them, a past that none of them has ever spoken about. Their recollections of it are all frighteningly different. So what really happened?

In pursuit of the truth, one of them uncovers an extraordinary secret and suddenly realises that they are all in mortal danger…

When I created the character of Harry Barnett for my fourth novel, Into the Blue, published in 1990, I had no inkling he would return in a sequel, Out of the Sun, six years later. His second return, in Never Go Back, another ten years on, was less of a surprise to me, because I’d been keeping track of him in the interim and sensed it was only a matter of time before he strayed unwittingly into another mystery. Despite his notoriously idle lifestyle, Harry is something of a magnet for mysteries and here he is again, out of his depth and struggling to escape dangers he would have run a million miles from if only he’d known they were lying in wait for him in the first place.

Harry has been a favourite of many of you ever since he made his first appearance and I’m very fond of him as well. He’s excellent (if somewhat boozy) company and his instinctive reaction to crises – a mixture of panic and stubborn resistance – is so close to my own that writing about him is always a pleasure. His scapegrace former friend and business partner, Barry Chipchase, is in many ways Harry’s alter ego and I felt the time had come to reunite them, technically old men now but still young (and in Barry’s case criminally feckless) at heart. Revelations in the media concerning experiments carried out on National Servicemen by the Ministry of Defence in the 1950s, some with fatal consequences for the subjects, sparked an idea in my mind as to how Harry and Barry’s early days together in the RAF could, unknown to them, contain a deadly secret.

So it is not just Harry and Barry who are reunited in this story, but many of their old RAF comrades as well. The action begins with a fiftieth anniversary gathering of their unit at the castle in Aberdeenshire where they were based. But the gathering has a sinister purpose. Uncovering what that is will put all those involved in mortal peril. And it will not be long before they all wish they had heeded the sound advice: never go back.