Fair warning - this is not my usual kind of book. I'm not usually a fan of cold-war thrillers, but it was the supernatural element that drew me in here - and I'm so glad I did!

First off, the atmosphere is perfect. Not a submarine (I have no way of commenting on that!); the sense of a winter in 1980s Europe, with the Berlin Wall firmly in place, Thatcher and Reagan fighting the USSR and everyday people just trying to get on. Including those who are essentially social outcasts (in this case both half-German and gay).

Protagonist Heidi (aka Thistle) is by no means a regular spy. She does her work to the best of her ability, while also battling considerable espionage PTSD and relationship grief over a lost girlfriend. Entering the claustrophobic, 100% male British environment of the HMS Viking sub is not an ideal mission. However, diving deep to discover a Russian nuclear vessel that shouldn't be there, Thistle discovers far more concerning drama than she could ever have anticipated.

This was a wonderful adventure that I tore through in two days. Essentially 'Event Horizon aboard Das Boot', it ramps up the tension from the get-go, moving from nuclear fear to something far darker that should've stayed in the depths of the ocean. Descriptions of life aboard a submarine - the conditions, the food, the smell! - had me entirely on board (pun intended), with the loneliness of the weird empty TK-15 pulling on even more nerves.

The characters are all fantastically drawn. I genuinely cared for Heidi/Thistle and understood why she would want to return to a terrifying place to save a fallen comrade even as I was internally shouting 'No, don't do it!'. Little touches such as photographs, the constant reminiscing about sunlight and dry land, and a stunningly effective piece of misdirection halfway through meant I couldn't leave the mystery unresolved any more than our messed-up heroine. I fully believe that life on board a submarine would make one question just what is reality, and this adds to that mental dilemma for the strangest, most compelling discomfort!

This is a truly remarkable book that achieves everything it sets out to do. More from Benedict Anning soon, please!