In early 1942, five letters were written and mailed by seemingly different people in different U.S. locations to the same person at an address in Buenos Aires, Argentina. Even more strangely, all of them bounced “Return to Sender”—and the “senders” on the return address (women in Oregon, Ohio, Colorado, and Washington state) knew nothing about the letters and had not sent them.

The FBI learned about all this when wartime censors intercepted one letter postmarked in Portland, Oregon, puzzled over its strange contents, and referred it to cryptographers at the FBI Laboratory. These experts concluded that the three “Old English dolls” left at “a wonderful doll hospital” for repairs might well mean three warships being repaired at a west coast naval shipyard; that “fish nets” meant submarine nets; and that “balloons” referred to defense installations.

One of the letters, supposedly sent by a Mary Wallace of Springfield, Ohio, did indicate her home address – 1808 E High Street – but had been postmarked in New York, a place she had never been. The letter, primarily discussing dolls, contained references to a “Mr. Shaw, who had been ill but would be back to work soon.” The letter corresponded to information that the destroyer USS Shaw, which had been damaged in the Pearl Harbor attack, completed repairs on the West Coast and was soon to rejoin the Pacific Fleet.

Another letter, given to the FBI in August of that year and said to have been written by a woman in Colorado Springs, Colorado, was postmarked from Oakland, California. That letter, written in February, made reference to seven small dolls which the writer stated would be altered to look as though they were “seven real Chinese dolls”, designed to mimic a family of parents, grandparents and three children. The FBI determined that the letter was written shortly after a convoy of ships had arrived at the Mare Island Naval Shipyard in Vallejo. The letter contained certain details about the ships, that if made public, would have been detrimental to the war effort.

The FBI immediately opened an investigation.

It was May 20, 1942, when a woman in Seattle turned over the crucial second letter. It said, “The wife of an important business associate gave her an old German bisque Doll dressed in a Hulu Grass skirt…I broke this awful doll…I walked all over Seattle to get someone to repair it….”

In short order, the FBI turned up the other letters. It determined that all five were using “doll code” to describe vital information about U.S. naval matters. All had forged signatures that had been made from authentic original signatures. All had typing characteristics that showed they were typed by the same person on different typewriters. How to put these clues together?

It was the woman in Colorado who provided the big break. She, like the other purported letter senders, was a doll collector, and she believed that a Madison Avenue doll shop owner, Mrs. Velvalee Dickinson, was responsible. She said Ms. Dickinson was angry with her because she’d been late paying for some dolls she’d ordered. That name was a match: the other women were also her customers.

Who was Velvalee Malvena Dickinson? Basically, a mystery. She was born in California and lived there until she moved with her husband to New York City in 1937. She opened a doll shop on Madison Avenue that same year, catering to wealthy doll collectors and hobbyists, but she struggled to keep it afloat. It also turned out that she had a long and close association with the Japanese diplomatic mission in the U.S.—and she had $13,000 in her safe deposit box traceable to Japanese sources.

Following her guilty plea on July 28, 1944, Ms. Dickinson detailed how she’d gathered intelligence at U.S. shipyards and how she’d used the code provided by Japanese Naval Attaché Ichiro Yokoyama to craft the letters. What we’ll never know is why the letters had been, thankfully, incorrectly addressed.