
A mysterious Parisian love letter: "It all started in Paris," filmmaker Doug Block tells CNN Travel. He was on vacation there with his wife, a romantic celebration of their 30th wedding anniversary. Walking along the Seine, the couple opened their second-hand copy of "Paris Walks" -- "Out pops this envelope with the name 'Betty' on it; it just fluttered to the floor, almost in slow motion," recalls Block. Pictured here: The letter, the envelope and the guidebook

Serendipitous discovery: "I opened it up, it's not sealed, and there's a museum card with a Monet painting on the front," says Block. Neither Block nor his wife knew the origin of the letter -- or where they had got this second-hand guidebook. They were struck by the heartfelt note, which referenced Paris' Musée d'Orsay. Pictured here: The notecard and its origins.

The triumph of love: The couple spent their second day in Paris traversing the halls of the Musée d'Orsay, admiring Monet's striking Impressionist paintings. That evening, Friday 13 November 2015, Paris was rocked by a series of deadly attacks. "The love letter hit home, the timing of it, in terms of everything that Paris was going through and the whole response internationally to the terrorist attack," says Block. Pictured here: Musée d'Orsay clock, Paris, France.

Ghostly figures: This unexpected discovery lifted Block's spirits -- a reminder of the power of love in the face of adversity. Back in his native New York, he found himself often coming back to "Betty" and "Henri", the writer of the letter. "It kind of haunted me," he recalls. Eventually he decided to get to the bottom of the mystery -- and attempt to find the couple behind the postcard. Pictured here: The letter from Henri to Betty.
![<strong>The quest begins</strong>: But how do you go about tracking down two people, based only on first names and handwriting? Some friends of Block and his wife thought they might have lent them the book -- they knew a Betty. Block went to visit her: "It was not Betty, but it was a remarkable Betty," says Block. "She was 91 years old. She spoke very candidly about her love life [...] I just felt like, I think I'm going to find a whole succession of Bettys and Henris in this search." <em>Pictured here: Musée d'Orsay, Paris, France.</em>](https://media.cnn.com/api/v1/images/stellar/prod/171102103111-gettyimages-522430502.jpg?q=w_4896,h_3264,x_0,y_0,c_fill/w_1280)
The quest begins: But how do you go about tracking down two people, based only on first names and handwriting? Some friends of Block and his wife thought they might have lent them the book -- they knew a Betty. Block went to visit her: "It was not Betty, but it was a remarkable Betty," says Block. "She was 91 years old. She spoke very candidly about her love life [...] I just felt like, I think I'm going to find a whole succession of Bettys and Henris in this search." Pictured here: Musée d'Orsay, Paris, France.
![<strong>Universal yearning for romance: </strong>It's this universality that's key to the appeal of Block's quest: "Betty and Henri are pretty much everyone," says Block. "Everyone no matter what their age has this yearning for romance, even if they've been married for many years, it doesn't extinguish this flame [...] I think this letter taps into it for most anybody I've come across."." <em>Pictured here: Paris skyline.</em>](https://media.cnn.com/api/v1/images/stellar/prod/171102102936-gettyimages-511152254.jpg?q=w_4884,h_3256,x_0,y_0,c_fill/w_1280)
Universal yearning for romance: It's this universality that's key to the appeal of Block's quest: "Betty and Henri are pretty much everyone," says Block. "Everyone no matter what their age has this yearning for romance, even if they've been married for many years, it doesn't extinguish this flame [...] I think this letter taps into it for most anybody I've come across."." Pictured here: Paris skyline.

International quest: Block hired a private investigator for tips, but his quest to find Betty has gone much further. "It's gone to a forensic analysis and a handwriting expert, a historical novelist who wrote a book about Monet," he says. He also visited a psychic. Pictured here: Paris at sunset.

Monet movie: Filmmaker Block has been documenting his quest as he goes along, preparing material for a future movie. Block has even filmed the original Monet painting in Washington's National Gallery of Art. Pictured here: "Woman Seated under the Willows," National Gallery of Art, Washington D.C, USA.

Reaching out: Block is no closer to discovering the real Betty and Henri: "It became clear to me that it's a real long shot finding Henri and Betty," says the filmmaker. "But the search is really the heart of the film." Nevertheless, Block remains hopeful -- and encourages anyone who recognizes the handwriting to contact him on Twitter. Pictured here: Musée d'Orsay, Paris, France.

Enduring appeal: Block thinks its also the mystery at the heart of the story that appeals: "The story just seems to connect with everyone, this idea of the kind of message in a bottle aspect of it, of this note somehow getting into this book, somehow ending up in my hands," he reflects. "The beautiful sentiment that's expressed in the letter. The mystery of the notecard and whether there's a connection, Monet is somehow involved, his connection with the story. It's just fascinating. I think people just love a good mystery." Pictured here: painter Claude Monet beside the water lily pond in his home garden, Giverny, France, 1910s.