Donath, Stanley F. "The Statue in the Fog"

An Austrian refugee nurse sets sail aboard a Cunard liner for America, along with hundreds of other refugees. As the unnamed liner zig-zags across the Atlantic, she briefly falls in love with a fellow traveler, a supposed Hungarian escaping the Nazis. After their ship is attacked at sea, she realizes that he is a really German agent and, choosing honor and loyalty over love, she turns him in to the naval authorities in charge of the liner.