The novel “Sinister Barrier” by Eric Frank Russell was published for the first time in 1939 in the magazine “Unknown” and in 1943 as a book in a revised and expanded version.

Bill Graham is shocked when two scientists his agency has funded die within a short time. A quick investigation leads him to discover that they were two of the many scientists who have recently died, and that some of them appeared to have gone mad. This situation immediately raises his suspicions.

When he turns to the police, Bill Graham is met with skepticism because there’s no evidence that the scientists were murdered, but Lieutenant Art Wohl helps him uncover other cases, making such a coincidence highly unlikely. Gathering fragments of information, the two of them discover that Peder Bjornsen had identified the presence of strange creatures, visible only in infrared light, which appear to be able to control humans.