On Sir Alfred Jarnock's estate in South Kent, there is a chapel rumored to be haunted. It is said that any enemy who enters the chapel after nightfall will be struck down by the dagger that rests over the altar. Engraved upon the dagger's sheath is an image of Christ crucified and the phrase, in Latin, "Vengeance Is Mine, I Will Repay." After the estate's butler falls victim to the alleged curse, the lord of the manor's eldest son calls Thomas Carnacki to investigate.

Against Sir Jarnock's wishes, Carnacki sneaks into the chapel one night with his camera, ready to get to the bottom of the mystery. But after a night of strange noises and a terrifyingly close call, Carnacki makes a surprising discovery.

"The Thing Invisible" was the final short story of Carnacki the Ghost Finder published during the author's lifetime.