Autumn 1952. Former First Lady and celebrated human rights advocate Eleanor Roosevelt is embarking on a transatlantic voyage to Paris in her role as a United Nations delegate, accompanied by her loyal young secretary Kay Thompson. Unfortunately they are also accompanied by a ruthless killer...

President Truman has announced he will not seek reelection, which means Mrs. Roosevelt will step down as a UN delegate. This will be her last voyage to Paris for the United Nations, but she and Kay are traveling in style aboard the S.S. United States, an ocean liner as large as the Chrysler Building on its side. In addition to delegates and dignitaries, there are Hollywood celebrities amongst the passengers: Cary Grant, as debonair and charming in real life as he is on the silver screen, and an up-and-coming starlet, Victoria Logan.

Typecast as a platinum blond sex symbol, Victoria is determined to take charge of her career by penning her own script, based on a true story of a woman murdered on a transatlantic liner whose body was dropped out her cabin porthole into the sea. When Kay discovers Victoria missing, her room in disarray and her porthole open, she fears life has imitated art. Cary Grant questions whether the scene has been staged as a publicity stunt with Victoria hiding somewhere on board. Mrs. Roosevelt encourages everyone not to leap to conclusions as she surveys the cabin for clues.

Soon after, a body is discovered on the ship-but it's not Victoria Logan. Now the only thing that's clear is they are all trapped in the middle of the Atlantic with a murderer, and Kay fears Mrs. Roosevelt herself may be a target . . .