Without Mercy by Jack Higgins

As Detective Superintendent Hannah Bernstein of Special Branch lies recuperating in the hospital, an enigmatic shadow from the past, burning with hatred, steals into her room and finishes the job. Consumed by grief and rage, Dillon, Blake Johnson, and all who loved Hannah swear vengeance, no matter where it takes them. But they have no idea of the searing journey upon which they are about to embark—or of the bloody war into which they are about to charge. Filled with dark suspense, driven by characters of complexity and passion, Without Mercy once again proves that Jack Higgins is the unchallenged master of international intrigue.