I believe I have mentioned this before, but just in case I have not: Antony Johnston has a frankly superb new book coming out, called The Coldest City.
If you enjoyed Tinker, Tailor, Soldier, Spy or Queen and Country, or The Sandbaggers, then you need to acquire this as soon as it comes out. A youtube trailer for the book is embedded below.
Go forth and buy it at once. All of you.