It is anything but quiet aboard the U.S. Navy submarine SS-495, the USS Saddleback. She’s on reduced battery power, nestled in the soft mud of the North Sea somewhere off the coast of Lower Saxony. It is the middle of World War II. Your mission has gone awry, your boat is sunk, and the horrible groaning of the tortured pressure hull has mixed with another sound—something stranger, more unearthly—from outside the submarine. And it is getting closer. You’re trapped in a stranded submarine and you have to get the hell out of here... before it comes in!