The seventh book in the Robicheaux series

Not many people believe this, but in the early months of 1942 Nazi submarines used to lie in wait at the mouth of the Mississippi for the tankers that sailed without naval escort from the oil refineries at Baton Rouge into the Gulf of Mexico.

It was a shooting gallery. Because of wartime censorship the newspapers and radio carried no accounts of the American ships sunk off the Louisiana coast, but just after sunset people could see the oil fires burning on the southern horizon, like a quickening orange smudge low in the winter sky.

As a little boy in New Iberia, I heard shrimpers talk about the burned, oil-coated bodies of four merchant sailors who had been found floating like lumps of coal in an island of kelp, their sightless eyes and poached faces strung with jellyfish.

I had nightmares for many years about Nazis, who I imagined as pinch-faced, slit-eyed creatures who lived beneath the waves, not far from my home, and who would eventually impose a diabolical design upon the earth.

While scuba diving in college, on a calm, windless day, I accidentally found one of those submarines in sixty feet of water, resting at an angle on its keel, the deck rails and forward gun gray and fuzzy with seaweed, a chain of tiny-bubbles rising from the stern.

My heart was tripping against my rib cage, the blood vessels tightening in my head, but I refused to be undone by my childhood fears, and I swam down to the twisted remains of the periscope until I could see the swastika and ship's numbers painted on the side of the conning tower.