Detective Bill Crane and his sidekick Doc Williams are hired by John Essex who has been receiving threatening letters, they are sent to his uncle's country estate to investigate and soon enough his sister Linda is kidnapped.
In 1937, Universal Pictures made a deal with the Crime Club, who were published of whodunnits.[3][4] Over the next few years Universal released several mystery films in the series.[3]The Last Warning was part of the series, and the last to feature the sleuthing team of Crane and Doc.[4]