You'd Better Believe It — Bill James

The first title in the popular Harpur and Iles series.

Harpur's domain is a small seaport city south of London. It's not unusual for the big-town criminals to consider such a spot as easy prey. At such times a policeman must rely keenly upon his colleagues, to be sure, and also upon his retinue of narks. This time it's a Lloyd's Bank branch that's the target. When the heist is postponed, a policeman is killed. One nark, then another, is murdered.

As Harpur becomes driven to his limit, he must bypass regulations and settle things once and for all with a vicious crook named Holly. But not necessarily on his own terms.