Emerald Decision — Craig Thomas

A British agent uncovers a secret nest of Nazi submarines. German agents multiply in Ireland. A Massive Nazi parachute drop is imminent somewhere in the British Isles.
CODE NAME EMERALD is put into effect - a secret plan so lethal and so illegal that all traces of it must be obliterated and all evidence buried.
One of the best British Intelligence agents lost his life in this secret action. The war over, a top American author seeks information for his bestseller. His quest spells death, danger and violence, and at the heart of it all, lies the mystery of his father.