Black Cross by Greg Iles

It is January 1944. The whole world awaits the Allied invasion of Europe. But in England, Winston Churchill has learned that Nazi scientists have developed Sarin—a horrifying new weapon that could turn the tide for Hitler. Only a desperate gamble can avert disaster.

Two men—a pacifist American doctor and a fanatical Jewish assassin—must embark on a murderous mission into the heart of Germany. Their target: a human hell where Jews fuel Hitler's last hope for victory. Their only allies: a young Jewish widow fighting to save her children and a German nurse who is the picture of Aryan perfection. Their orders: destroy the threat no matter how many lives are lost, including their own...