Jigsaw — Campbell Armstrong

In Campbell Armstrong's explosive thriller, Detective Frank Pagan fights terrorism on his home turf, where a deadly female assassin has infiltrated London's elite social circles

When a bomb detonates in the London Underground, killing dozens of people, Scotland Yard asks counterterrorism expert Frank Pagan to come back from leave. With none of the usual suspects claiming responsibility, Pagan has a hunch that Carlotta, the world's deadliest female terrorist, is responsible. Then a US embassy employee goes missing, and Frank's investigation takes a new direction. Was the presumed terrorist bombing actually an assassination attempt?
 
Now Pagan is up against a shadowy group known as the Undertakers as he tries to untangle a lethal web of deceit involving a philanthropist leading a double life that includes a mysterious woman, deadly KGB agents, a semiretired member of the East German Stasi, and the US ambassador himself.

Jigsaw is the 4th book in the Frank Pagan Novels, but you may enjoy reading the series in any order.