This is an understated, pleasant little film based on the true story of Elsie Wright and Frances Griffiths, cousins living together in Cottingley England, who shot five photographs of fairies starting in 1917. The girls were 16 and 9 at the time but in the film are depicted as several years younger. Arthur Conan Doyle believed the photos to be genuine and wrote a fair amount about them. He’s portrayed in the film by Peter O’Toole.
Doyle was for a long while friends with the Harry Houdini despite their opposing views on Spiritualism and the supernatural. I don’t think Houdini actually had much to do with the Cottingley fairies, but he has a prominent place in the film in the person of Harvey Keitel, who is excellent in the role, playing a friendly skeptic.
The film shows the fairies as real but never shows the photographs being taken and also reveals cutouts of fairies that clearly could have been used to fake the images, leaving it up to the viewer to decide whether the fairies shown are real or depictions of the girls’ imaginations.
The real Elsie and Frances confessed in their 80s that they’d faked four of the five pictures with cutouts held up by hat pins. But both women maintained until the end that they really had seen fairies and that the eerie final photograph (which you can find in the Wikipedia article on the Cottingley fairies at this link) was genuine.