A bookmaker with a fancy for detective work attempts to prevent the execution of a potentially innocent man.

二战初期，丹麦商船 “海尔维格号” 船长安徒生（康拉德・韦特饰）因英国港口管制滞留伦敦。他在码头邂逅自称索伦森夫人（瓦莱丽・霍布森饰）的神秘女子，对方以寻找失踪丈夫为由，请求安徒生协助。
两人卷入一场德国间谍阴谋：间谍头目范戴恩（雷蒙德・洛威尔饰）企图窃取英国海军机密，索伦森夫人实为英国情报人员，正卧底调查。安徒生凭借机智与勇气，与船员、英国特工联手，在伦敦的夜总会、码头与间谍展开周旋，最终挫败间谍计划，救出索伦森夫人。
故事融合悬疑、动作与浪漫，以轻松幽默的笔触展现战时伦敦的紧张氛围，安徒生从普通船长转变为反间谍英雄，成为影片亮点。

In Britain, a man with a shady past uses his antiquities shop as a front for smuggled diamonds but his young shop-assistant starts blackmailing him, leading to murder and to a police investigation.