New York, 1915. RMS Lusitania, one of the world's most luxurious ocean liners, departs for war-torn Europe. Among those on board is Patrick Gallagher, a civil servant in His Majesty's government tasked with escorting a British diplomat back to England. When a fellow passenger is believed to have shot himself in his cabin, Gallagher is asked by the captain to investigate the scene - but one crucial detail doesn't fit. The man's body was discovered...