Playwright Robert Kenyon, his wife, and secretary are staying at their cottage in Littleworth. Also present is Kitty Lake, a friend and actress. One night Kitty is brutally murdered in the study, and there is no sign of the murderer.
Superintendent Arthur Sinclair happens to be working nearby, and he and the local man Sergeant Curtis begin investigations. Sinclair stays the night in the cottage, but the next day he is called off to another case in India and Curtis takes over. The circumstantial evidence collected leads the police to arrest a man for the murder. But, in the absence of Arthur Sinclair, will an innocent man hang? '2.L.O.' tells the story of Sinclair’s final case before he retired from Scotland Yard.

About the title:
Listening to the radio gained rapidly in popularity during the 1920s, and crime writers, as usual, soon identified the potential of a pleasingly topical new setting for their mysteries. Walter S. Masterman duly published 2LO in 1928—the title refers to a station which began broadcasting from Marconi House in 1922, and was transferred to the newly created British Broadcasting Company the following year.
--Martin Edwards, Miraculous Mysteries, 2017