Michael Gilbert 
Game Without Rules [PDF ebook] 

Mr. Calder lived with a golden deerhound named Rasselas in a cottage in Kent. Mr. Behrens lives with his aunt and keeps bees. No one would in the least suspect that the pair are in fact agents for the British Joint Services Standing Committee and they are often tasked with jobs that no one else can take on – simply because of the extreme nature of the action needed. They are dangerous – and they are watched. Their adventures in this series of thrillers show the author to have a clear grasp of counterintelligence operations. Written with Gilbert’s usual dry wit, panache and style, the suspense is at times killing!