Looking for a spy thriller that is genuinely terrifying

Hi all,

Looking for a spy thriller recommendation that is serious and genuinely tense.

Most spy books I come across feel a bit too entertaining or action-movie like. I’m specifically looking for something that feels realistic and intense, where the stakes feel very high and you actually feel fear and real concern for the protagonist.

Ideally something that:

Feels grounded and believable (not over-the-top gadgets or unrealistic action)

Has a constant sense of danger or paranoia

Makes you feel like the protagonist might actually fail or die

Focuses on psychological tension, espionage, surveillance, betrayal, etc.

Basically a spy thriller that is stressful to read in the best way, not “fun spy adventure”.

If you’ve read something that made you feel uneasy or genuinely worried for the character, I’d love to hear your recommendations.

Thanks!