Sheila Bennet returns to New York from Cuba carrying $40,000 worth of smuggled diamonds - and smallpox, which could start a devastating epidemic in the unprotected city. Treasury agent Johnson loses her but keeps doggedly on the trail; while Public Health doctor Wood searches in vain for the unknown person spreading the deadly disease far and wide. Meanwhile, the increasingly ill Sheila is concerned only with her faithless husband Matt, who plans to abscond with the diamonds.