It's the height of World War II. Mary and Paul Strong keep house in their Greenwich Village apartment and look forward to the letters from their friend Max, a news photographer on assignment in Iceland. But when the next letter arrives it turns out to be a series of blank pages with a Canadian theater program inside. That evening they hear the news-the boat Max is on is torpedoed by a German sub, with all hands lost.

Paul knows something is terribly amiss, but can make nothing of the strange clue Max has mailed them. Mary herself is very suspicious of their new upstairs neighbors, then learns some very startling information on her own. Paul decides to catch the next ship to Iceland. Mary decides to stowaway on Paul's ship, and both of them are headed for the adventure of their life.